Jonathan A. Chu

August 28, 2017

Every armed humanitarian intervention since the end of the Cold War has been conducted

under the auspices of an international organization (IO). Some authors explain this striking

observation by pointing to the ability of IOs to mobilize mass support for war. Building on

these domestic approaches, this article develops and tests a novel theory of how IOs influence

public opinion. It argues that IOs can win citizen policy approval by sending cues about the

social repercussions of military intervention, but such cues can only be effectively sent by IOs

that represent the political identities held by citizens. Evidence from historical polls and

original survey experiments regarding American opinion on humanitarian war validate the

theory’s claims. The findings contribute to debates on the domestic channels of IO influence,

the value of multilateralism in foreign policy, and the role of identity in world politics.

Jonathan Chu is a Ph.D. candidate in the Department of Political Science at Stanford University

(jonchu@stanford.edu). I thank Kirk Bansak, Matthew Baum, Songying Fang, Moritz Marbach, Mark

Jacobsen, Risa Kitagawa, Steve Krasner, Melissa Lee, Philip Lipscy, Adam Liu, Julia Payson, Phil Potter,

Jonathan Renshon, Piki Ish-Shalom, Ken Schultz, Paul Sniderman, Mike Tierney, Mike Tomz, and panel

participants at Stanford, UC Merced, ISA, HEWG, MPSA, APSA, PSS, and EPSA for their feedback. I am

also grateful for the support of Stanford’s Laboratory for the Study of American Values and the NSF Graduate

Research Fellowship (Grant #DGE-114747). All views and errors remain my own. Stanford IRB Protocol

#32333.

Humanitarian wars are almost always conducted under the auspices of an international

organization (IO).1 But why would countries, especially superpowers like the United States,

bother seeking the approval of an IO? After all, the process of obtaining institutional

authorization could limit a government’s policy autonomy, and in cases like Rwanda and Syria,

inaction in light of IO opposition could allow the brutal slaughter of innocent lives.

On this question, a flourishing research agenda finds that governments prize IOs for

their role in winning the policy approval of domestic audiences.2 When an IO recommends a

policy, citizens are more likely to support that policy, and political leaders care because popular

opinion often translates to votes during elections, perceptions of foreign policy competence,

and clout in other political arenas.3 The extant scholarship outlines two main reasons why IOs

can sway mass opinion on war. Legal approaches claim that IOs, depending on their status in

international law, can grant legal legitimacy on the use of force.4 In contrast, rationalist

approaches contend that IOs, depending on their membership’s preference distribution, can

signal information about the material consequences of a policy.5 By investigating the domestic

channels through which IOs affect international affairs, these authors make a fundamental

contribution to theories of international institutions, which have traditionally focused state-to-

state channels of IO influence.6

To advance the scholarship on the domestic politics of IOs, this paper develops and

tests a new explanation for how IOs affect mass opinion. Drawing from theories of social

identity and socialization,7 it argues that policy recommendations by IOs serve as cues about a

policy’s social repercussions and appropriateness. An IO’s policy endorsement answers

1 Finnemore 2003, chapter 3; Schultz 2003 2 Schultz 2003; Chapman and Reiter 2004; Tago 2005; Voeten 2005; Fang 2008; Thompson 2009; Chapman

2011; Grieco et al. 2011; Tingley and Tomz 2012. 3 Hurwitz and Peffley 1987; Aldrich, Sullivan, and Borgida 1989; Gartner, Segura, and Barratt 2004; Gelpi

et al. 2009; Gelpi and Grieco 2015. On the effect of public opinion on foreign policy in democratic countries

more generally, see Risse-Kappen 1991; Sobel 2001; Holsti 2004; Aldrich et al. 2006; Weeks 2008; Stein

2014; Baum and Potter 2015; Milner and Tingley 2016. 4 Koh 1997; Tago and Ikeda 2015, 392. 5 Thompson 2009; Chapman 2011. 6 E.g. Keohane 1984; Abbott and Snidal 1998; Hurd 2008. 7 E.g. Johnson 2008; Abdelal et al. 2009.

question such as, does the policy (i.e. humanitarian intervention) represent pro-norm behavior?

Will peer countries participate to advance the policy? Will enacting this policy improve my

nation’s status and reputation? The theory further argues the ability of IOs to send these social

cues depends on the political identities they represent. Citizens are thus more susceptible to

IOs with which they identify.

This article examines this argument in the context of how the UN Security Council

(UNSC) and NATO affect U.S. public opinion on humanitarian war. The conventional wisdom

implies that the UNSC is crucial for garnering public support. After all, only the UNSC can

satisfy international legal requirements, and because it sparingly authorizes war, its policy

recommendations arguably indicate that military force is merited and will have good

consequences. The social identity view alternatively hypothesizes that the UNSC is not so

crucial. For citizens of liberal democracies like the U.S., NATO embodies the collective identity

shared by a broader democratic community,8 while the UNSC represents a more diffuse group of

countries. This democratic identity thus empowers NATO to send social cues about the

appropriateness of intervention, regardless of the UNSC, which in turn shapes mass opinion.

For evidence, this study analyzes historical polls since the end of the Cold War and a

series of original public opinion experiments that disentangles the effects of NATO and the

UNSC on American policy attitudes, along with the causal mechanisms that explain their

influence. The core of these studies are vignette-based surveys in which American citizens read

about a civil conflict abroad, and then express their support for U.S. military intervention to

save foreign lives. Based on experimental assignment, different survey takers receive different

information about whether the IOs endorse or renounce the use of force.

Validating the theory, the analysis demonstrate that NATO sways mass opinion

regardless of the UNSC’s policy position. These effects hold true even among liberal

internationalists, the politically sophisticated public, and those who are informed about

international law. To undertake the challenging task of assessing causal mechanisms, the

analysis employs three distinct empirical strategies to show that NATO’s influence over public

opinion is indeed due to social identity factors. Together, the evidence supports the argument

8 Deutsch et al. 1957; Risse-Kappen 1995.

that IOs can mobilize popular support for humanitarian intervention because of the collective

identities they represent.

This article brings a fresh perspective to the question of how and why IOs affect mass

attitudes: the domestic power of IOs rests on social foundations, as opposed to legal or material

ones. By making this theoretical contribution, the argument also contributes to the study of

how domestic norms and identities affect international relations.9 Stephen Krasner recently

wrote that “There are only three big causal factors in the study of politics: material interests,

physical power and security, and ideas/identities/norms. We understand the first two pretty

well, but not the third.”10 The theory and evidence thus help meet this shortage.

Making empirical contributions as well, this study employs the first research design to

experimentally measure the independent effect of NATO, meeting the call of many researchers

to explore institutions beyond the UNSC.11 Studying NATO alongside the UNSC not only

sheds light on the two most important security institutions in U.S. foreign policy, but also

provides the empirical variation in IOs that is much-needed for theory testing. Such a study

design additionally helps to overcome inferential issues relating to causal inference and the

lack of consistent and theoretically-relevant data. The conclusion further discusses the paper’s

empirical and theoretical contributions.

This study explains American public opinion on humanitarian war. It joins a growing

scholarship that focuses on the external factors that explain mass attitudes.12 Such literature

demonstrates that policy cues from international institutions influence the opinions of domestic

audiences even after accounting for domestic political cues.13

9 Work on public opinion, norms, and war include Herrmann and Shannon 2001; Gelpi 2002; Press, Sagan,

and Valentino 2013. 10 Krasner 2016. 11 Thompson 2006, 30; Grieco et al. 2011, 571; Fang 2008, 314. 12 Others, in contrast, examine individual-dispositional (Kertzer et al. 2014) or domestic-level (Zaller 1992;

Berinsky 2009) sources of policy preferences. 13 Grieco et al. 2011; Hayes and Guardino 2013; Guardino and Hayes n.d.

On these topics, one prominent research agenda investigates the role of IOs as

“information providers” to citizens.14 These theories observe that policy makers hold a

disproportionate amount of knowledge in international affairs, and thus, mass publics face an

information deficit when evaluating foreign policy. Furthermore, citizens might not be able to

trust the recommendations of their leaders, who could be promoting a policy for parochial

reasons.15 Given this dilemma, people might turn to IOs to obtain a “second opinion” about a

policy’s merits.16 Explained from a different angle, elites who cannot credibly convince their

publics that a policy is worth undertaking may turn to an external source of policy validation.

This literature generally agrees that IOs can persuade citizens to support war, but

scholars debate why this is the case. Various theories provide different explanations for two

fundamental questions. First, what about an IO allows it to sway mass opinion? Second, when

an IO recommends a policy, what is it communicating to the cue-recipient? Legal and

rationalist approaches provide distinct answers to these two questions.

From the legal perspective, an IO is able to sway mass opinion due to its status under

international law. Under international law, the UNSC has broad authority to sanction the use

of force to address threats to international peace and security. According to this doctrine, only

the UNSC can legalize humanitarian war.17 Other IOs like NATO. Americans might be

influenced by legal considerations for several reasons.18 First, UNSC authorization might

signal to citizens that a humanitarian crisis poses a “threat to international peace and security,”

and inaction would allow the crisis to spread across national borders. Second, legal norms

diffuse and are internalized by citizens, especially those who live in a country with a legalistic

culture that respects the rule of law.19 Thus, people might consider an IO-sanctioned policy to

hold “legal legitimacy.”20

14 Fang 2008; Thompson 2009; Chapman 2011; Grieco et al. 2011; Tago and Ikeda 2015. 15 Fang 2008. 16 Grieco et al. 2011 17 This interpretation is supported by treaty law, the words of governments, and legal scholars (Frank 2002). 18 Of course, law does not work exclusively through publics. For example, law could shape policy via

centralized agencies (König and Mäder 2015). 19 Chong 1993; Koh 1997; Finnemore and Sikkink 1998; Goodman and Jinks 2013; Hafner-Burton,

LeVeck, and Victor 2016 20 Tago 2005, 589; Tago and Ikeda, 392.

Citizens could also care about the law for instrumental reasons. Guzman (2008)

outlines “three Rs of [international law] compliance”: reciprocity, reputation, and retaliation.

The U.S. is unlikely to face reciprocity for waging an illegal humanitarian war, but it could

face reputation loss and foreign retaliation. Tomz (2008) shows that American and British

citizens and elites are more supportive of economic sanctions against a law-violating country

than against an otherwise identical country that respects the law, and this “law effect” is

partially channeled through reputational concerns. On retaliation, Voeten (2005, 528) proposes

that “when governments and citizens look for an authority to legitimize the use of force…they

want political reassurance about the consequences,” which includes punishment by powerful

countries.21 Thus, Americans might believe that an unsanctioned intervention could damage

national reputation or provoke other countries to punish the U.S.

Turning to a rationalist perspective, other authors claim that an IO’s ability to influence

citizen attitudes depends on the preference distribution of its membership. A prominent variant

of this argument claims that the most persuasive cues are given by conservative or independent

IOs.22 In particular, a conservative IO is one whose pivotal member is ideologically distant

from the country seeking authorization. Based on this criterion, these theories explicitly

hypothesize that the UNSC should have a greater effect on American attitudes than NATO.23

Similar arguments are made about the role of IOs in convincing foreign publics, arguing that

neutral IOs (i.e. IOs that are comprised of a diverse set of countries) are also more persuasive

when it comes to reassuring skeptical citizens.24

These theories also provide insight into the content of an IO’s cue. Because citizens

are uncertain about a politician’s true motivations for proposing war, they worry that war will

lead to bad outcomes.25 When an IO recommends the use of force, it is letting citizens know

that the policy will have “desirable consequences,” and that a policy will “not be exceedingly

costly or overly aggressive.”26 On the flip side, an IO’s endorsement could also signal the

21 Voeten does not advance a “theory of international law,” but his argument fits with Guzman’s framework. 22 These authors draw from models of cheap talk and models on the role of legislative committees (e.g.

Crawford and Sobel 1982; Gilligan and Krehbiel 1989). 23 Chapman 2011, 51-56. 24 Thompson 2009. 25 Fang 2008. 26 Thompson 2009, 33; Chapman 2011, 7.

benefits of a policy. For example, a humanitarian intervention will actually save lives, and an

intervention into a civil war will actually generate stability.

The existing literature lends insight into the domestic politics of IO influence, but several

empirical anomalies reveal the need for new theory building and empirical investigation.

Calling into question the legal perspective, in 1999 the United States and NATO allies

conducted armed humanitarian intervention in Kosovo without the approval of the UNSC. But

rather than condemning the U.S., the international community—including some many lawyers

who should be the most-likely political actors to care about legality—declared the illegal

intervention to be nevertheless legitimate (Independent International Commission on Kosovo

2000). Furthermore, public support for Kosovo, as an analysis later in this paper will show,

was at levels similar to cases in which both the UNSC and NATO endorsed intervention (e.g.

Libya). In terms of the rationalist argument, several studies call into question both the idea that

IOs lead citizens rationally update their beliefs about the material costs of war,27 and the

premise that an IO’s conservativeness or membership diversity affects an IO’s ability to

persuade domestic audiences.28 Collectively, these anomalies imply that researchers have yet

to fully explain how IOs affect citizen attitudes.

This section proposes a new theory on the role of IOs in influencing mass foreign policy

preferences. Like the legal and rationalist perspectives, it begins with the premise that domestic

audiences look to international cues when forming their attitudes toward foreign policy, and

that governments can leverage foreign cues to mobilize public support. The main point of

departure, however, is to focus on the role of identity and social context.29 This implies that

people look to the judgments of IOs for cues about the social, rather than the legal or material,

implications of a particular policy. I develop this theoretical intuition through three claims: the

27 Tingley and Tomz 2012. 28 Fey, Jo, and Kenkel 2015; Hainmueller, Mummolo, and Xu 2017, 25-8; Chu 2017. 29 Johnston 2008; Abdelal et al. 2009

democratic community reflects a collective identity shared by its citizens, and policy

endorsements by this community are social cues, and IOs facilitate the sending of these cues.

At this point, the idea that like-minded cue givers are more persuasive might echo theories

of heuristics in political behavior.30 In the context of domestic elite cues, these theories argue that

people look to the policy positions of elites whom share their policy interests as a way to quickly

evaluate whether a policy fits their preferences. The social theory here builds on these insights, but

as the discussion below makes clear, it provides a distinct rationale for why like-minded endorsers

shape mass preferences.

In the context of U.S. humanitarian intervention, what exactly is the relevant social context?

At least since the Cold War, people from liberal democracies like the U.S. have come to

associate with one another. Indeed, a long tradition of research on political communities argues

that the U.S. is embedded in a global community of democracies, especially with regards to

NATO.31 Two features of this community are relevant to understanding the political influence

of IOs.

One facet of the democratic identity—and of any identity—is the norms that define or

constitute it.32 In general, those who are part of an identity-sharing community follow a “logic

of appropriateness” or share a set of beliefs about how they should behave.33 These beliefs

might be codified into formal rules or exist informally as commonly understood expectations

or a “community of practice.” For the liberal democratic community, governments and their

citizens adhere to norms of consultation and norms against coercive bargaining,34 though these

norms do not necessarily apply to interactions with governments outside the club of

democracies.35 Importantly, the norms of consultation highlight the need for collective

30 E.g. Calvert 1985; Lupia and McCubbins 1998 31 Deutsch et al. 1957; Risse-Kappen 1995; Adler and Barnett 1998; Hemmer and Katzenstein 2002 32 Finnemore 1996; Katzenstein 1996b; Adler 1997; Wendt 1999 33 March and Olsen 1998 34 Risse-Kappen 1995; Adler 2008, 204-6 35 Doyle 1986; Maoz and Russett 1993; Tomz and Weeks 2013

deliberation the club of democracies when conducting foreign policy,36 and this process is often

institutionalized within an IO.

Second, people sharing an identity are also defined by their “relational comparisons.”37

This aspect of identity helps to answer the question, what are the characteristics of others that

we do not hold or practice that define who we are? Just as the Cold War experience constructed

a sense of community among democracies, it also demarcated those who did not belong—

countries with authoritarian government, closed economies, and a lack of basic rights.

Together, these features delineate both an in- and out-group in international affairs.38

Even after the Cold War, the democratic identity remains, and it embodies a normative

institution that continues to shape politics. For example, Herrmann and Shannon (2001, 642)

show that in-group identity among advanced democracies explain people’s support for war,

and Risse-Kappen (1996) finds that the existence of a democratic community explains why

NATO persists even though structural conditions predicted its collapse. Reflecting on the

enduring nature of political identities, Peter Katzenstein observes that political actors “attribute

far deeper meanings to the historical battles that define collective identities than to the transient

conflicts of daily politics.”39

How does the theoretical discussion thus far shed light on the way in which the UNSC

and NATO shape American attitudes toward humanitarian intervention? It implies that

Americans considering whether or not to support humanitarian intervention will value, first

and foremost, endorsements from within their social group and thus of other liberal democratic

36 This literature already explores the historical formation of the democratic identity, so for space I focus on

the implications of this identity rather than its origins. 37 Abdelal et al. 2009, 20-4 38 This discussion is compatible with psychological approaches to group identification (e.g. Mercer 1995;

McDermott 2009). 39 Katzenstein 1996a, 3. Whether U.S. President Donald Trump’s rhetoric has fundamentally shifted

American identity in world politics (for some people) remains an open question. It is worth noting that after

Trump assailed NATO during his campaign, the U.S. congress reacted by bringing forth a bipartisan

resolution to affirm the U.S.’s commitment to NATO (Accessed 5/31/16 at:

http://foreignpolicy.com/2016/05/18/exclusive-in-rebuke-of-trump-house-resolution-defends-nato/). A

PEW study also found that “[w]hile Trump recently called into question the value of U.S. participation in

NATO, Americans overwhelmingly view NATO membership as beneficial for the United States…Large

majorities in both parties say NATO membership is good for the U.S.” (Accessed 6/14/16 at:

http://www.people-press.org/2016/05/05/public-uncertain-divided-over-americas-place-in-the-world/). In

any case, the theory does not clam that identities last forever, and the conclusion revisits the idea of identity

change.

countries. These in-group cues are most prevalently captured by the policy endorsements of

NATO, which is emblematic of the liberal democratic community.40 On the other hand, after

the core community is consulted, cues from out-group countries or IOs with more diffuse

representation like the UNSC do not substantially shape popular opinions. Once the democratic

community-via-NATO has taken a stance on intervention, Americans are unlikely to place

much weight on additional judgments from the UNSC.

The process of socialization sheds light on the mechanisms through which political

communities affect people’s policy preferences.41 In particular, I argue that policy judgments

by IOs send social messages, cuing those with a particular identity as to whether adopting a

particular policy is appropriate or will produce positive social (in contrast to material)

outcomes.42 What does it mean, though, to send a cue about a policy’s social appropriateness

and implications?

Drawing from socio-psychology and political science, Johnston (2001) outlines two

microprocesses that are a part of the socialization of individuals: persuasion and social

influence. Persuasion “involves changing minds, opinions, and attitudes about causality and

affect (identity) in the absence of overtly material or mental coercion,” which includes the

changing of attitudes via cues or endorsements (496-7). Meanwhile, social influence “refers to

a class of microprocesses that elicit [intersubjectively understood] pro-norm behavior through

the distribution of social rewards and punishments,” where the rewards and punishment affect

one’s status or image rather than material outcomes (499-501).43 As a result of persuasion and

social influence, community members are convinced or feel pressured to adopt a certain policy,

participate in group activities, and be seen as engaging in pro-norm behavior.

40 NATO, of course, does not perfectly represent the liberal democratic community. It largely represents (and

certainly more so than the UNSC) the club of democracies. 41 Johnston (2001, 494) defines socialization as “the process by which social interaction leads novices to

endorse ‘expected ways of thinking, feeling, and acting.’” While Johnston focuses on the socialization of

“novices,” I treat socialization as occurring continuously even after members have adopted a shared identity. 42 Existing research finds that IOs are central to facilitating socialization (e.g. Finnemore 1993; Li 2010). 43 Johnston (2008, 80) notes that persuasion involves changing another’s beliefs about what is right, while

social influence is a form of peer pressure that changes behavior without changing internally held beliefs.

But this paper does not attempt to identify the particular proportion of each process that constitutes the ability

of IOs to shape public opinion.

This discussion implies that when NATO recommends a particular foreign policy (e.g.

humanitarian intervention), it engages in persuasion and social influence for those holding the

liberal democratic identity. More concretely, cues from NATO answer questions such as, how

will engaging in this policy affect my country’s status or reputation?44 Will others in my group

collectively act to advance this policy? Does pursuing this policy conform to pro-norm

behavior for countries like mine? In the case of humanitarian war, pro-norm behavior includes

championing liberal values in international affairs, which encompasses stopping human rights

violations. These factors, in turn, elicit support for intervention.

The ability of IOs to influence domestic audiences is rooted in the collective identities and

community of countries they represent. What political purpose, then, does an IO serve beyond

their member states? Firstly, IOs are fora that help disparate community members coordinate

and centralize their decision making,45 which implies that individual governments may fail to

reach a group decision without a formal organization. Additionally, IOs may increase the

accessibility of a foreign cue. Americans might be more likely to hear the policy platform of a

country via an IO than that of the same country announcing its policy position on its own

outside of an IO. From this point of view, IOs do not add anything substantive to a groups’

policy message. Instead, the IO’s primary role is to make sure a community of countries

successfully comes together to make the policy recommendation in the first place and that the

recommendation is accessible to domestic audiences.

IOs, however, do more than facilitate coordination. This paper argues that social cues

reveal the implications of a foreign policy on the likeliness of collective action, reputation and

status, and beliefs about pro-norm behavior: IOs can amplify each of these social mechanisms.

An IO facilitate monitoring and enforcement, which could increase the likeliness of collective

action to fulfil a policy.46 Enforcement in the case of NATO takes the form of social

sanctioning, implying that IOs raise the reputational stakes of not going along with a group

44 Because this study does not attempt disentangle the instrumental and non-instrumental reasons for valuing

status (Johnston 2008, 82-84; Renshon 2016), it uses the more colloquial definition of “reputation” to

encompass all forms of status. 45 Keohane 1984; Abbott and Snidal 1998. 46 Martin 1992.

activity like humanitarian intervention.47 Lastly, when individuals make a policy endorsement,

it may not be clear whether they are doing so because of their identity or because of other

unrelated interests. If an IO symbolizes a particular identity (such as in the way NATO

symbolizes a community of liberal democratic countries), then recommending a policy via an

IO could clarify the social meaning of that recommendation.

This discussion implies that members of the democratic community can sway the

opinion of the American public, but they are more influential when they voice their views via

NATO. Contrast this with the alternative theories. The international law argument highlights

the legal authority held by the IO itself, rather than the IO’s members. Thus, a cue from a group

of countries will have little influence if it is not sent through an IO. Meanwhile, information

theories argue that the strength of an informational cue is a function of the distribution of

preferences held by an IO’s component countries, which implies that the informational content

of a cue from a group of a countries versus the same group of countries acting through an IO

is about the same.

This study evaluates three principal claims derived from the community identity theory: (1)

NATO’s policy position sways mass support for humanitarian intervention, independently of

the UNSC’s stance, (2) NATO affects public opinion via causal mechanisms relating to the

social repercussions and appropriateness of intervention, and (3) liberal democratic countries

affect American public opinion, but their influence is magnified when sent via NATO.

The main evidence comes from four survey experiments, but before turning to the experimental

design, it is useful to assess these claims in light of observational data. While relying on

historical polls raises many inferential problems (e.g. strategic selection, missing data, etc),

they motivate the experimental design and buttress the external validity of the larger study.48

Table 1 allows us to assess a few descriptive patterns in the historical relationship

47 Johnston 2008 48 Driscoll and Maliniak (2016) gives an example of validating experiments with observational data.

between the UNSC, NATO, NATO’s countries, and support for humanitarian war.49 It includes

cases in which the U.S. considered humanitarian intervention and opinion polls were available.

Column 1 names the case. Columns 2 through 4 gives the policy position of the NATO’s

countries, NATO and the UNSC. NATO’s policy position on intervention is generally

equivalent to policy position of its member countries. But when NATO did not consider the

case of intervention (i.e. NATO = N/A), the country positions is coded using public statements

and actions of NATO’s member states. Column 5 then gives the percentage of respondents that

supported intervention (unreported are those who opposed war or responded “don’t know” or

“no opinion”). The right most column gives the average support for intervention at different

degrees of international policy endorsement. The data are from the Roper Center database.

Detailed information on the polls along with coding notes are in Appendix C.

The record reveals three broad classes of humanitarian interventions. Interventions

with little international support (e.g. Syria), ones in which NATO and the club of democracies

support intervention but the broader international community vis-à-vis UNSC does not

(Kosovo), and interventions with widespread international backing (Bosnia). Public opinion in

these three groups suggest that Americans prefer war with international backing over wars

without it. Only 28 to 31 percent of Americans supported intervention without foreign

approval, while a majority of Americans supported interventions with some degree of IO

approval. Interestingly, Americans do not reveal a preference for interventions with both

UNSC and NATO approval over interventions with only NATO approval.50 These patterns are

consistent with the identity theory’s prediction that once a cue from the in-group is received

(i.e. NATO), the additional cue from other countries has little effect.

49 The polls specifically ask for people’s support for military intervention for humanitarian reasons. They do

not include commonly asked but less relevant questions like, “Do you agree with how President Clinton is

handling the situation in Somalia?” 50 Libya might be classified as a “NATO Only” intervention because the UNSC’s resolution arguably did not

cover the NATO airstrikes against Qaddafi.

Table 1: Past National Polls on American Support for Intervention

Cases Support Intervention? % Supporting War

NATO Countries NATO UNSC By Case Average

Rwanda 1994

Syria 2013

No (minus France)

No

N/A

No

No

No

28

33 31

Kosovo 1999

(Libya 2011)

Yes

(Yes)

Yes

(Yes)

No

(No)

53

(56)

53

(55)

Somalia 1992

Haiti 1994

Bosnia 1994

Libya 2011

Yes (Strong)

Yes (Weak)

Yes

Yes

N/A

N/A

Yes

Yes

Yes

Yes

Yes

Yes

74

34

57

56

55

Note: This table summarizes data from historical surveys conducted during episodes of potential

humanitarian intervention. NATO is coded N/A in when the case was considered “out of area” at the

time. The Rwanda poll was taken prior to France’s Operation Turquoise, which received UNSC

approval. The Libya case might be classified under “NATO Only” because the UNSC resolution

arguably did not cover the NATO airstrikes.

These polls provide initial evidence for the identity theory, but they nevertheless face

major shortcomings and speak to the need for an alternative research design. First, the historical

data cannot account for the problem of selection bias. It is likely that U.S. decisions to seek IO

approval are a function of domestic politics, which could frustrate inference about the effect of

IOs on public opinion. Second, there are many factors that explain both the policy positions of

IOs and public opinion, and these “omitted variables” confound the observed relationship

between IOs and public opinion. For example, both IOs and citizens could form their opinions

based on the merits of intervention rather than the policy positions of each other. Third, many

of the cases have idiosyncratic features. Somalia, for example, was the U.S.’s first

contemporary case of humanitarian intervention just after the popular First Gulf War. These

factors, rather than the fact that there was virtually unanimous international consensus on

intervention, might explain the high levels of public enthusiasm for intervention in Somalia.

Finally, historical polls generally lack information useful for analyzing causal mechanisms,

which is essential for evaluating and building theory.

To overcome the problems arising from solely analyzing historical polls, this study deploys a

novel experimental design. Conducting an experiment that randomly and independently

assigns the policy cues of IOs overcomes the problem of selection and causal inference. And

designing original survey questions creates an opportunity to measure key variables regarding

the causal mechanisms that explain how IOs persuade citizens.

Specifically, this study conducted a series of experiments inserted into four public

opinion polls fielded in the United States. Surveys #1 through #3 help test the claims about the

effect of IOs and the causal mechanisms through which policy cues influence Americans, while

Survey #4 evaluates the effect of cues sent by the democratic community with and without an

NATO. I describe the first three surveys here and revisit Survey #4, which has a slightly

different design, in a later section. The surveys were administered online from January 2015

to April 2016. Survey #1 was conducted via YouGov to a nationally representative sample of

Americans, while Surveys #2 and #3 were given to diverse but convenience samples via

Amazon Mechanical Turk (MTurk).51 Appendix A gives the respondent attributes.

In the surveys, respondents read about a humanitarian crisis in which “Military groups

fighting in [country] have killed thousands of civilians, including women and children, and

have left tens of thousands homeless and starving.” In Survey #1, the target “[country]” was

randomly selected from the following five potential target countries: Azerbaijan, Burma,

(Myanmar), Chad, Colombia, and Yemen. In Surveys #2 and #3, the country was either

Azerbaijan or Chad. These countries have a history of civil conflict, which helps to deepen the

study’s realism and political relevance. The five countries also represent different regions so

that the result could inform a range of cases. In the statistical analyses, data across these

different potential country scenarios are pooled together, but results conditional on the target

country are given in Appendix D.52

Next, respondents read about the UNSC and NATO’s stance on humanitarian war. In

Survey #1, respondents were randomly assigned to read one of three potential scenarios that

mirror the historical record presented in Table 1: both IOs oppose intervention (None), only

NATO supports intervention (NATO Only), and both IOs endorse intervention (Both). In

Survey #2, respondents read all three scenarios plus a fourth scenario in which only the UNSC

but not NATO supports intervention (UNSC Only). The fourth scenario is unprecedented

historically, but this “off-equilibrium” case is useful for evaluating theory, which is discussed

fully in the analysis. In Survey #3, respondents were assigned to read either the None or NATO

Only scenarios, and several additional experiments were embedded into this survey to better

understand the how people process information about international law and material outcomes.

To increase realism and external validity, respondents also received information about the key

countries belonging to each IO.53 But note that Survey #4 will disentangle the effect of naming

countries versus naming the IOs.

Finally, respondents in each survey expressed their attitudes toward the use of force by

answering the following: “In this situation, do you support or oppose the US sending its

51 Research shows that MTurk samples produce findings that are comparable to more representative samples

(Berinsky, Huber, and Lenz 2012). 52 The country is independently assigned and thus does not confound estimates of the effect of IOs.

Randomizing the country, however, adds variance to the dependent variable, which actually makes detecting

statistically significant effects less likely. 53 News articles on the UNSC and NATO generally mention key countries from the IOs. For example, when

the UNSC authorizes the use of force, news often report the voting record of the P5 in the article lede.

military to help civilians in [country]?” There were six replies: support or oppose a little, a

moderate amount, or a great deal. People’s answers to this question formed the study’s main

dependent variable, Support for Intervention. Appendix B contains the full questionnaire.

Note that the forthcoming analysis compares levels of the dependent variable across

the treatment groups, often using the None condition as a baseline group. The experimental

design did not implement a group in which respondents receive no information about either

IO. Respondents in such a “no information” condition are free to assume, either consciously or

subconsciously, whatever they wish about the main explanatory variable, IO Support. This is

highly problematic. IOs have approved of virtually all contemporary humanitarian

interventions, and both NATO and the UNSC recommended the recent intervention in Libya.

Given these facts, many respondents are likely to assume a degree of IO endorsement, either

because people use analogies to reason through hypothetical scenarios or because people

subconsciously associate the concept of humanitarian intervention with NATO and the UNSC.

This could generate respondent non-compliance, driven by respondents who, in a sense, “treat”

themselves with the IO endorsement.54 Thus, the surveys explicitly informed respondents the

positions of each IO to avoid this design flaw.55

Data from Survey #1 allow us to estimate the main effect of IOs on mass opinion. For clarity,

I analyze the dependent variable, Support, in its binary form (i.e. either support or oppose the

use of force), but the results are robust to using the full 6-point scale. Table 2 shows that moving

from a war that NATO and the UNSC oppose (None) to one that is endorsed by NATO but not

the UNSC (NATO Only) heightens Support by 26.4 percentage points. The 95 percent

confidence interval indicate that this increase is statistically distinguishable from zero at the

54 Chu 2016 55 In contrast, see Johns and Davies (2014). This study employs a rich survey of British opinion on war, but

for its experiment on IOs, informs respondents that either NATO or the UN supports war. However, hearing

“UN supports war” does not imply that NATO opposes wars, and vice versa. Thus, the fact that the UN and

NATO have recently supported policies in tandem could explain why the study finds similar levels of support

between these experimental conditions.

0.05 level. By contrast, the additional impact of the UNSC’s endorsement (moving from NATO

Only to Both) is both substantively small (4.3 points) and statistically insignificant.

These results largely mirror the historical data presented in Table 1, speaking to the

external validity of the findings. Further bolstering the validity of these findings, a joint

endorsement by NATO and the UNSC raises support for war by about 30 points, which

replicates the results from a previously published nationally representative survey conducted

via telephone.56 Finally, these results are robust to limiting the sample of respondents to groups

that are particularly influential in American foreign policy: the sophisticated public and liberal

internationalists (see Appendix D).57 This suggests that the effect of IOs is not driven by policy

ignorance or people who do not engage with international affairs.

56 Grieco et al. 2011, table 3 57Wittkopf (1990, Ch. 5) finds that elites are more internationalist than the general population. Milner and

Tingley (2016) find that liberal internationalists form a coalition that drives U.S. foreign policy.

Table 2: NATO Increases Support for Intervention but

a Security Council Endorsement Adds Little More

Treatment

Group

% supporting

intervention

(Support)

Difference in %

supporting

intervention

None

N=354

48.3

[43.0, 53.6]

26.4

[19.4, 33.4]

4.3

[-2.2, 10.8]

NATO Only

N=332

74.7

[69.6, 79.3]

Both

N=314

79.0

[74.1, 83.4]

Note: This table gives the percent of respondents supporting

intervention for each treatment group, and the difference in

support between groups. “None” indicates an endorsement from

neither NATO nor the UNSC. “NATO” is an endorsement from

only NATO. “Both” is an endorsement from both IOs. 95%

confidence intervals are reported in brackets. N=1,000. Data are

from Survey #1.

Next, Survey #2 allows us to rule out an alternative interpretation of the main results,

that Survey #1’s results reveal a first-versus-second cue giver effect rather than a NATO-

versus-UNSC effect. Put another way, there could be diminishing returns to policy cues, and

so any second cue (not just the UNSC’s) will have little influence on public opinion. In Survey

#2, respondents are assigned to one of four experimental groups: the original three scenarios

(None, NATO Only, and Both), and a fourth scenario in which only the UNSC endorses

intervention (UNSC Only). Figure 1 presents the results and reveals two key patterns. First, the

original three treatment groups replicate the results from Survey #1. The effect of moving from

None to NATO is large, while the additional endorsement from the UNSC is insubstantial.

Second, and in contrast, the UNSC alone only slightly raises enthusiasm for war (from None

to UNSC), but NATO’s additional recommendation still substantially boosts intervention

support (from UNSC to Both). Finally, the data allow us to calculate the effect of each IO

averaging across the other IO’s policy positions. The effect of NATO is 15.7 points and the

effect of UNSC is 6 points, and the difference is statistically significant.

Figure 1: NATO Has a Greater Effect on Public Attitudes

than the UN Security Council

Note: This figure shows the proportion of respondents supporting

intervention for four experimental group. “None” indicates an

endorsement from neither NATO nor the UNSC. “NATO” is an

endorsement from only NATO. “UNSC” is an endorsement from only the

UNSC. “Both” is an endorsement from both IOs. 95% confidence

intervals are given. N=408. Data are from Survey #2

Analysis reported in Appendix D shows that NATO’s influence on public opinion

remains even under conditions designed to confirm the legal and information theories’

hypotheses. Beginning with the legal perspective, respondents’ knowledge about international

law should presumably suppress the effect of NATO while amplifying the effect of the UNSC,

but this is not the case (Figure A3). A follow-up experiment further shows that NATO’s

influence remains even after respondents are explicitly informed that the UNSC is necessary

for intervention to be legal (Figure A4). Lastly, the information theories argue that the more

conservative an IO, the greater effect that IO should have on public opinion, where

conservativeness is measured using the IO’s pivotal member’s ideological distance from the

cue-receiver. However, Table A5 show that the effect of NATO and UNSC are not conditional

on respondents’ perceptions about each IO’s pivotal member.

The investigation thus far shows that NATO affects mass support for humanitarian intervention

regardless of the UNSC’s position. It now evaluates additional implications of the identity

theory by assessing the causal mechanisms that explain how NATO affects public opinion. The

identity theory argues that, because American identify with NATO’s member-countries,

NATO raises support for intervention by revealing the social implications of deploying military

force, which include national status and reputation, collective action, and perceptions of norm

conformity. These mechanisms contrast with factors relating to international law, information

transmission, and other material or burden sharing variables.58 To be clear, these mechanisms

are not mutually exclusive, but they are useful to distinguish in the analysis.

I employ three empirical strategies to evaluate these mechanisms. First, I examine an

assumption about the subgroups among which the mechanisms should be most relevant:

Americans who identify with NATO’s members. Second, I conduct mediation analysis to

directly estimate the relevance of various mechanisms.59 Third, I indirectly assess the

importance of the social mechanisms by ruling out alternative causal pathways.

58 But note that Recchia (2015) argues that the burden sharing mechanism is primarily about convincing the

military elite to support intervention. 59 Imai et al. 2011

The identity theory implies that NATO’s effect is largest among Americans who mostly closely

identify with NATO’s members and thus care most about the social cues that NATO delivers.

Using data from Survey #2, I test this hypothesis by analyzing NATO’s average endorsement

effect conditional on country affinity, which I use as a measure of shared identity. To measure

affinity, respondents reported their opinions about whether the following four countries “share

a friendly, neutral, or hostile relationship with the U.S.”: Canada, Germany, France, and the

United Kingdom.60 I split the sample in half based on people’s average affinity of these four

countries, creating a dummy variable Affinity, which takes the value 0 among those who feel

relatively distant and a value of 1 among those who feel relatively close to these countries.

To analyze whether Affinity moderates NATO’s endorsement effect, I use a probit

model to regress Support on NATO, Affinity, and their interaction, along with a set of

demographic and political control variables. Figure 2 reports the results (control variable

estimates are in Appendix E). Starting at the top, it shows that NATO’s effect on Support

among the regression’s baseline category, people who express relatively low affinity toward

NATO’s countries, is about 5.4 percentage points (i.e. a 0.054 change in the probability of

supporting intervention), though this effect is not statistically significant. A NATO cue absence

of affinity has a trivial effect. The interaction term, however, indicates that the effect of NATO

is significantly larger among people who express relatively high affinity (19 points larger).

60 I also asked about China and Russia. Together, this encompasses two countries that are only in NATO,

only in the UNSC, and in both IOs. Data from all six countries are used in supplementary analysis in

Appendix D.

Figure 2: NATO’s Effect is Strongest among Americans

who Identify with NATO’s Members

Note: This figure reports the marginal predicted probabilities from

probit coefficients. The dependent variable takes a value of 0 if the

respondent opposes intervention, and a value of 1 if the respondent

supports intervention. The baseline category is the condition in which

NATO opposes intervention and respondents express low affinity toward

NATO’s members. Control variables (gender, age, education, party ID,

and ideology) are reported in Appendix E. 95% confidence intervals are

given. N=408. Data are from Survey #2

.054

-.0009

.19

NATO

Affinity

NATO*Affinity

-.4 -.3 -.2 -.1 0 .1 .2Change in Probability of Supporting Intervention

Next, I analyze six causal mechanisms that might explain NATO’s endorsement effect.

Reputation measures perceptions about whether intervention would improve or damage the

U.S.’s reputation.61 Collective Action indicates respondents’ beliefs about whether other

countries will contribute to military action. Humanitarian Motives captures beliefs about

whether intervention conforms to pro-norm behavior: that is, whether the U.S. is actually using

force for humanitarian reasons. Prevent Contagion indicates expectations about whether not

intervening would lead a spread of conflict. Retaliation Unlikely records beliefs about whether

other countries would punish the U.S. for using military force. Casualties Unlikely measures

expectations about American war casualties.

Recall that the identity theory implies that all three social considerations, Collective

Action, Reputation/Status, and Humanitarian Motives (pro-norm behavior), are significant

mediators. It also argues that fears about foreign retaliation should not vary due to democratic

norms against coercive diplomacy. The other mechanisms relating to Contagion, Retaliation,

and Casualties are not predicted by the theory but are included in the analysis for a point of

comparison.

With these hypotheses in mind, the causal mediation analysis proceeds in three steps:

estimate the effect of NATO Only on each mediator; estimate the effect of each mediator on

the dependent variable, Support for Intervention; and finally using information from the first

two steps, estimate the average mediation effects.

Figure 3 displays the results from steps one and two. For each mediator, the left panel

shows the effect of moving from None to NATO Only. The estimated probit coefficients are

reported in terms of predicted probabilities. When NATO recommends intervention, people

are more likely to believe that intervention benefits U.S. Reputation, leads to Collective Action,

and is for Humanitarian reasons. Next, NATO’s policy judgements make people believe that

war can Prevent Contagion, and that Retaliation and Casualties are Unlikely; however, the

effect of NATO on Retaliations Unlikely and Casualties Unlikely is small and statistically

insignificant. The right panel illustrates the effect of each mediator on Support. The mediators,

unlike the IO cues treatment, are not experimentally varied, so I include control variables (not

61 These six variables are measured using data from Survey #1 and further described in Appendix E.

reported in the figure) to guard against confounding from omitted variables.62 All of the

mechanisms are positively associated with popular support for the use of force, but to different

degrees. Reputation has the largest effect, while concerns about Retaliation have the smallest

effect.

Figure 3: Potential Explanations for how NATO Shapes Public Opinion

Note: This figure gives the predicted marginal effects from probit coefficient estimates. The left panel

plots the marginal NATO effect on six mediators, and right panel plots the effect of those mediators on

people’s intervention support, controlling for potential confounds. Estimates from the control variables

are not displayed. Each of the 12 estimates is obtained from a separate regression. 95% confidence

intervals are given. Data are from Survey #1.

62 The control variables are gender, age, education, income, race, religion, ideology, party identification,

voter registration, internationalism, beliefs about human rights, and news interest.

Combining these two steps provides the basis for estimate each mechanism’s mediation

effect. Specifically, the analysis executes the procedures outlined in Imai et al. (2011) using

statistical software programmed by Hicks and Tingley (2011).63 Table 3 gives the average

mediation effect for each mechanism. Recall that NATO raises Support by 26.4 percentage

points. The analysis shows that 6.4 of those points are mediated by concerns about Reputation.

In other words, some of NATO’s effect on public opinion is channeled through people’s beliefs

about how intervention affects U.S. reputation or status. The results also demonstrate that

concerns about Collective Action, Humanitarian (Motives), and Contagion are significant

causal pathways, but beliefs about Retaliation and Casualties are not.

Consistent with the identity theory, the analysis shows that people’s social concerns

about Reputation, Collective Action, and Humanitarian Motives are important causal links. The

policy position of NATO sends a social cue to Americans. Unpredicted by the theory, concerns

about Contagion also explain the effect of NATO. Finally, concerns about Retaliation and

Casualties do not mediate the effect of NATO on attitudes.64 The null finding for Retaliation

finding is predicted by the identity theory. In sum, the mediation analysis rules out the

relevance of the casualties and retaliation mechanisms, and shows that social appropriateness

mechanisms largely explain how NATO sways public opinion.65

63 Appendix E gives a technical overview of this analysis. 64 The Casualties finding might seem counterintuitive. But to clarify, it does not contradict the conventional

wisdom that casualties affect public opinion (e.g. Mueller 1973; Gartner 2008). Figure 3 shows that

Casualties do indeed affect Support, but NATO endorsements do not change beliefs about Casualties. 65 Note that the decreasing mediation effects from Reputation to Casualties is unlikely to be a result of

question ordering. These questions appeared in the following order: Reputation, Casualties, Retaliation,

Humanitarian, Collective Action, and Contagion. They are rearranged in this paper to be consistent with the

theoretical grouping.

Table 3: Social Mechanisms Explain

NATO’s Endorsement Effect

Mediator

Average

mediation

effect

Reputation/Status 6.4*

Collective Action 3.9*

Humanitarian 1.5*

Prevent Contagion 3.2*

Retaliation Unlikely 0.4

Casualties Unlikely 1.0

Note: This table shows the mediation effects

of six variables that might explain how NATO

raises support for intervention. Asterisks

highlight estimates that are significant at the

0.05 level. Data are from Survey #1.

The final analysis of causal mechanisms demonstrates that NATO’s endorsement effect

remains even after accounting for material or burden sharing factors, such as the number of

lives that would be saved, the financial and human costs of military action, and the mode of

intervention. To rule out these alternative factors, Survey #3 included the original experiment

in which NATO supports or opposes military action (NATO), while additionally randomizing

whether respondents received or did not receive information about the material cost and

benefits of military action (Information).66 If NATO boosts support for war via providing

information about the material consequences of military action, then directly providing that

information to respondents should dampen the effect of NATO. In other words, the interaction

of NATO and Information should have a negative effect on people’s support for war.

The analysis applies a probit model to regress Support on NATO, Information, and their

interaction (NATO*Information). Figure 4 displays the results of this analysis in terms of

predicted marginal probabilities. The estimate of NATO shows that, among those who are not

given information about material cost and benefits, a NATO endorsement increases Support

by 29 percentage points (or 0.29 increase in probability of supporting war). The negative

coefficent of NATO*Information indicates that informing respondents about material cost and

benefits reduces the NATO effect, but only by 4.4 points. This effect is also statistically

insignificant. Put another way, 85 percent of NATO’s effect on Support (i.e. (29-4.4) /29)

remains even among those who are informed about the number of lives at stake, financial costs

to the U.S., and mode of intervention. Thus, 85% of NATO’s effect must be due to other

mechanisms such as those relating to social considerations.

66 Those who received information read the following: “Military action would save the lives of about [80

thousand OR 620 thousand] civilians. The operation would cost the U.S. government about [$850 million

OR $4.1 billion], but the U.S. would avoid risking casualties by not sending ground troops.”

Figure 4: NATO’s Endorsement Effect is Not About Material Factors

Note: This figure reports the effect of NATO and information about the material

consequences of intervention on people’s support for war. The estimates are from a probit

regression and given in terms of predicted marginal probabilities. The outcome takes a

value of 0 if the respondent opposes intervention, and a value of 1 if the respondent

supports intervention. The baseline category is the condition in which NATO opposes

intervention and respondents receive no information about material consequences.

N=1,141. Data are from Survey #4.

.29

.036

-.044

NATO

Information

NATO*Information

-.2 0 .2 .4Change in Probability of Supporting Intervention

The community identity theory argues that the ability of IOs to shape public opinion comes

from their member countries, but those countries are more persuasive when operating through

an IO. Survey #4 helps to test this argument. As in the previous surveys, some respondents

were experimentally assigned to read that “The North Atlantic Treaty Organization (NATO)

[opposes/supports] taking military action to help these civilians. NATO members include the

U.S., Canada, and several European countries.” But to distinguish the effect of NATO from

the effect of its named countries, other respondents read that NATO supports/opposes military

action without mention of any particular country names, while others read that “U.S., Canada,

and several European countries” support/oppose military action without mention of NATO.

This creates six experimental groups (Both Countries and IOs, IOs Only, or Countries Only

either support or oppose military action). Because Surveys #1 through #3 establish that

NATO’s endorsement effect is independent of the UNSC, this version did not mention and

vary the policy position of the UNSC, which helps to increase statistical power for the NATO

experiment. As before, the dependent variable is people’s support for armed intervention.

Appendix A and B provide the sample attributes and survey questionnaire.

Table 4 presents difference in proportion of war support for each pair of experimental

treatments (e.g. difference in support when Countries Only supports intervention from when

Countries Only opposes intervention). As the identity theory predicts, the countries of the

democratic community alone can sway American attitudes (Countries increases support for

intervention by 15.5 points), but those same countries acting via NATO have an even greater

influence (Both has a 32.8 point effect). The effect of IO Only is included for analytical

completion, but is actually difficult to interpret. Even though it does not mention NATO’s

member countries, respondents can easily infer that several democratic countries support

intervention simply from hearing “NATO.” What this data does help to clarify, though, is

whether the effect of the policy cue relies primarily on naming countries. The results show they

do not: IO Only has a 24.8 point effect on intervention support.

Table 4: The Role of IOs versus their Countries

The endorsement effect of… Change in War Support in

Percentage Points [95% C.I.]

Countries Only 15.5 [3.4, 27.6]

IO Only 24.8 [12.3, 37.2]

Both Countries and IO 32.8 [20.0, 45.6]

Note: This table shows the effect of policy endorsements on people’s

support for intervention. N=598. Data are from Survey #4.

A vast majority of humanitarian wars are conducted with the backing of an IO. To explain this

vexing empirical regularity, scholars argue that governments value the blessing of IOs for their

ability to mobilize public support. This conventional wisdom explains the link between IOs

and public opinion by focusing on the ability of IOs to fulfill legal requirements or relay

information about a policy’s merits. This paper demonstrates that these approaches overlook

the social and ideational role of IOs. In the case of U.S. humanitarian intervention, liberal

democratic countries share a collective identity that allows NATO, independently of the

UNSC, to communicate the social appropriateness of the use of force and thus convince

Americans to support war.

This article presents evidence from historical polls and a unique set of experimental

studies that disentangles the UNSC and NATO’s effects on public opinion, and identifies the

causal pathways through which IOs influence domestic audiences. The data demonstrate that

policy recommendations by NATO rally American citizens for war, and the mechanisms that

explain this effect are people’s social affinities and considerations about reputation, collective

action, and pro-norm behavior. The analyses also present a variety of empirical tests to account

for alternative explanations.

Together, the contributions of this paper are both theoretical and empirical. The study

provides new insights on the domestic politics of IO influence, and it does so by developing

the first theory that connects social identities, mass opinion, and international institutions. The

findings also provide a new answer to the age old question of why do international institutions

appear legitimate. Existing theories explain institutional legitimacy in legal and rationalist

terms, while this paper finds that legitimacy has social foundations. Turning to the empirical

contributions, this study conducts and analyzes the first experiment to evaluate the independent

effect of an IO other than the UNSC. By examining NATO, the evidence sheds light on one of

the most important institutions in American foreign policy, and for the sake of theory testing,

it provides a point of comparison to the Security Council. The evidence also takes a multi-

faceted approach to assess the causal mechanisms that link IOs to public opinion. Lastly, by

showing that the experimental results are borne out in the historical data, the evidence can

address concerns about both internal and external validity.

The findings also sheds light on the nature of forum shopping in international relations.

In an insightful paper, Voeten (2001) observes that the UNSC since 1990 has rarely vetoed

resolutions regarding the use of force despite the existence of members like Russia and China

whose interests are generally against humanitarian wars. If the UNSC is so necessary, then

why do those Security Council members not simply exercise their veto? Through game

theoretic models, Voeten argues that the existence of a credible outside option leads Security

Council members to make policy concessions and refrain from exercising a veto. In the case

of humanitarian intervention, the most salient outside option is NATO. Why might NATO be

a credible outside option? And is there evidence for such an outside option? Addressing these

unanswered questions, this paper shows that NATO is a credible outside option to the UNSC

because it can fulfill the function of mobilizing domestic support for intervention, filling in a

long-neglected empirical gap in the literature on forum shopping in international security.67

This project has two natural extensions: assessing non-humanitarian wars and non-U.S.

public opinion. Regarding non-humanitarian wars, national security concerns could moderate

the effect of IOs. After all, the identity theory does not claim that social considerations override

all else. If security matters, then one hypothesis could be, the more the justifications for war

concern core national security interests, the smaller the effect of IOs. For example, in wars of

self-defense IOs will probably have little effect on enthusiasm for military action.68 Second,

the identity theory could generalize beyond the American context. Given the U.S.’s superpower

status and culture of exceptionalism among some Americans, the social effect of IOs would

presumably be even stronger when it comes to the democratic citizens of smaller countries.

Additionally, citizens of autocracies like Iran or China are unlikely to exhibit the same patterns

in their opinions when it comes to the endorsement of NATO. It would be useful for future

research test the theory in other countries to see if this is the case.

In terms of U.S. foreign policy, policymakers seeking to raise support for humanitarian

intervention should obtain multilateral support, though the form of multilateralism should first

and foremost contain the U.S.’s fellow liberal democracies. Once that support is gained,

obtaining UNSC authorization might be important for some people, but not the broader

67 Also see Lipscy (2017) for applications beyond the security realm. 68 However, Herrmann and Shannon (2001, 641) show that normative factors affect American elite support

for armed intervention even when material interests are threatened.

American public. The normative implications of these findings are for a different study, but

this paper’s findings imply that one way to influence global constraints on U.S. foreign

policymaking is via socialization. While Americans have held a stable liberal democratic

identity for over six decades, that identity is not timeless. Fostering a cosmopolitan American

identity might increase the sway that foreign political actors have on U.S. public opinion, while

promoting an identity of exceptionalism could have the opposite effect.

Abbott, Keneth W., and Duncan Snidal. 1998. “Why States Act through Formal International

Organizations.” Journal of Conflict Resolution 42 (3): 3–32.

Abdelal, Rawi, Yoshiko M. Herrera, Alastair Iain Johnston, and Rose McDermott. 2009.

Measuring Identity: A Guide for Social Scientists. New York, NY: Cambridge University

Press.

Adler, Emanuel. 1997. “Seizing the Middle Ground: Constructivism in World Politics.” European

Journal of International Relations 3 (3): 319-63.

Adler, Emanuel. 2008. “The Spread of Security Communities: Communities of Practice, Self-

Restraint, and NATO’s Post-Cold War Transformation.” European Journal of Political

Science 14 (2): 195-230.

Adler, Emanuel and Michael Barnett (eds.). 1998. Security Communities. New York, NY:

Cambridge University Press.

Aldrich, John H., John L. Sullivan, and Eugene Borgida. 1989. “Foreign Affairs and Issue Voting.”

American Political Science Review 83 (1): 123–141.

Aldrich, John H., Christopher Gelpi, Peter Feaver, Jason Reifler, and Kristin Thompson Sharp.

2006. “Foreign Policy and the Electoral Connection.” Annual Review of Political Science

9 (1):477-502.

Baum, Matthew A. and Philip B.K. Potter. 2015. War and Democratic Constraint: How the Public

Influences Foreign Policy. Princeton, NJ: Princeton University Press.

Berinsky, Adam J. 2009. In Time of War: Understanding American Public Opinion from World

War II to Iraq. Chicago, IL: University of Chicago Press.

Berinsky, Adam, Gregory Huber, and Gabriel Lenz. 2012. "Using Mechanical Turk as a Subject

Recruitment Tool for Experimental Research." Political Analysis 20: 351–368.

Brooks, Deborah J. and Benjamin A. Valentino. 2011. “A War of One’s Own: Understanding the

Gender Gap in Support for War.” Public Opinion Quarterly 75 (2): 27-86.

Calvert, Randall L. 1985. “The Value of Biased Information: A Rational Choice Model of Political

Advice.” Journal of Politics 47: 530-55.

Chapman, Terrence L. 2011. Securing Approval: Domestic Politics & Multilateral Authorization

for War. Chicago, IL: University of Chicago Press.

Chapman, Terrence and Dan Reiter. 2004. “The United Nations Security Council and the Rally

‘Round the Flag Effect.” Journal of Conflict Resolution 48 (6): 886-909.

Chong, Dennis. 1993. “How People Think, Reason, and Feel about Rights and Liberties.” American

Journal of Political Science 37 (3): 867-99.

Chu, Jonathan A. 2016. “Reciprocity, International Humanitarian Law, and American Attitudes

toward Wartime Torture.” Working Paper, Stanford University. Available at:

http://jonchu.weebly.com/research.html

Chu, Jonathan A. 2017. “Information Transmission by International Organizations: A

Reassessment.” Working Paper, Stanford University. Available at:

http://jonchu.weebly.com/research.html

Crawford, Vincent P. and Joel Sobel. 1982. “Strategic information transmission.” Econometrica

50: 1431-51.

Deutsch, Karl W., Sidney A. Burrell, Robert A. Kann, Maurice Lee Jr., Martin Lichterman,

Raymond E. Lindgren, Francis L. Loewenheim, Richard W. Van Wagenen. 1957. Political

Community and the North Atlantic Area: International Organization in the Light of

Historical Experience. Princeton, NJ: Princeton University Press.

Doyle, Michael W. 1986. “Liberalism and World Politics.” American Political Science Review 80

(4): 1151– 69.

Driscoll, Jesse and Daniel Maliniak. 2016. “Did Georgian Voters Desire Military Escalation in

2008? Experiments and Observations.” Journal of Politics 78 (1): 265-80.

Fang, Songying. 2008. “The Informational Role of International Institutions and Domestic

Politics.” American Journal of Political Science 52 (2): 304-321.

Fey, Mark, Jinhee Jo, and Brenton Kenkel. 2015. “Information and International Institutions

Revisited.” Journal of Conflict Resolution 59(1): 149-60.

Finnemore, Martha. 1993. “International Organizations as Teachers of Norms: the Untied Nations

Educational, Scientific, and Cultural Organization and Science Policy.” International

Organization 47 (4): 565-97.

Finnemore, Martha. 2003. The Purpose of Intervention: Changing Beliefs about the Use of Force.

Ithaca, NJ: Cornell University Press.

Finnemore, Martha and Kathryn Sikkink. 1998. “International Norm Dynamics and Political

Change.” International Organization 52 (4): 887-917.

Flores-Macias, Gustavo and Sarah E. Kreps. 2013. “Political Parties at War: A Study of American

War Finance, 1789-2010,” American Political Science Review 107 (4), 833-848.

Frank, Thomas M. 2002. Recourse to Force: State Action Against Threats and Armed Attacks.

Cambridge, UK: Cambridge University Press.

Gartner, Scott Sigmund, Gary M. Segura, and Bethany A. Barratt. 2004. “War Casualties, Policy

Positions, and the Fate of Legislators.” Political Research Quarterly 57 (3): 467-477.

Gartner, Scott Sigmund. 2008. “The Multiple Effects of Casualties on Public Support for War: An

Experimental Approach.” American Political Science Review 102 (1): 95–106.

Gelpi, Christopher, Peter D. Feaver, and Jason Reifler. 2009. Paying the Human Costs of War:

American Public Opinion and Casualties in Military Conflicts. Princeton, NJ: Princeton

University Press.

Gelpi, Christopher and Joseph Grieco. 2015. “Competency Cost in Foreign Affairs: Presidential

Performance in International Conflict and Domestic Legislative Success, 1952-2001.”

American Journal of Political Science 59 (2): 440-56.

Gilligan, Thomas W. and Keith Krehbiel. 1989. “Asymmetric Information and Legislative Rules

with a Heterogeneous Committee.” American Journal of Political Science 33 (2): 459-90.

Grieco, Joseph M., Christopher Gelpi, Jason Reifler, and Peter D. Feaver. 2011. “Let’s Get a

Second Opinion: International Institutions and American Public Support for War.”

International Studies Quarterly 55 (2): 563-83.

Goodman, Ryan, and Derek Jinks. 2013. Socializing States: Promoting Human Rights through

International law. New York, NY: Oxford University Press.

Guardino, Matt, and Danny Hayes. N.d. “Foreign Voices, Party Cues, and U.S. Public Opinion

about Military Action.” Working Paper. Available at: http://home.gwu.edu/~dwh/iran.pdf

Guzman, Andrew T. 2008. How International Law Works: A Rational Choice Theory. New York,

NY: Oxford University Press.

Hafner-Burton, Emilie M., Brad L. LeVeck, and David G. Victor. 2016. “How Activists Perceive

the Utility of International Law.” Journal of Politics 78 (1): 167-180.

Hafner-Burton, Emilie M., Brad L. LeVeck, David G. Victor, and James H. Fowler. 2014.

“Decision Making Preferences for International Legal Cooperation.” International

Organization 68 (4): 845-76.

Hainmueller, Jens, Jonathan Mummolo, and Yiqing Xu. 2017. “How Much Should We Trust

Estimates from Multiplicative Interaction Models? Simple Tools to Improve Empirical

Practice.” Working Paper, Stanford University. Available at SSRN:

https://ssrn.com/abstract=2739221

Hartley, Thomas and Bruce Russett. 1992. “Public Opinion and the Common Defense: Who

Governs Military Spending in the United States?” American Political Science Review 86

(4): 905–915.

Hayes, Danny and Matt Guardino. 2013. Influences from Abroad: Foreign Voices, the Media, and

U.S. Public Opinion. New York, NY: Cambridge University Press.

Hemmer, Christopher, and Peter J. Katzenstein. 2002. “Why is There No NATO in Asia? Collective

Identity, Regionalism, and the Origins of Multilateralism.” International Organization 56

(3): 575-607.

Herrmann, Richard K. and Vaughn P. Shannon. 2001. “Defending International Norms: The Role

of Obligation, Material Interest, and Perceptions in Decision Making.” International

Organization 55(3): 621-54.

Hicks, Raymond and Dustin Tingley. 2011. “Causal Mediation Analysis.” The Stata Journal 11(4):

1-15.

Holsti, Ole R. 2004. Public Opinion and American Foreign Policy, rev. ed. Ann Arbor, MI:

University of Michigan Press.

Hurd, Ian. 2008. After Anarchy: Legitimacy and Power in the United Nations Security Council.

Princeton, NJ: Princeton University Press.

Hurwitz, Jon and Mark Peffley. 1987. “How Are Foreign Policy Attitudes Structured? A

Hierarchical Model.” American Political Science Review 81(4): 1099-1120.

Hyde, Susan. 2015. “Experiments in International Relations: Lab, Survey, and Field.” Annual

Review of Political Science 18: 403-24.

Imai, Kosuke, Luke Keele, Dustin Tingely, and Teppei Yamamoto. 2011. “Unpacking the Black

Box of Causality: Learning about Causal Mechanisms from Experimental and

Observational Studies.” American Political Science Review 105 (4): 765-789.

Independent International Commission on Kosovo. 2000. The Kosovo Report. New York, NY:

Oxford University Press.

Johns, Robert, and Graeme AM Davies. 2014. “Coalitions of the Willing? International Backing

and British Support for Military Action.” Journal of Peace Research 51 (6): 767-781.

Johnston, Alastair Iain. 2001. “Treating International Institutions and Social Environment.”

International Studies Quarterly 45(4): 487-515.

Johnston, Alastair Iain. 2008. Social States: China in International Institutions, 1981-2000.

Princeton, NJ: Princeton University Press.

Katzenstein, Peter J. 1996a. Cultural Norms and National Security: Police and Military in Postwar

Japan. Ithaca, NY: Cornell University Press.

Katzenstein, Peter J., ed. 1996b. The Culture of National Security: Norms and Identities in World

Politics. New York, NY: Columbia University Press.

Keohane, Robert. 1984. After Hegemony. Princeton, NJ: Princeton University. Press.

Kertzer, Joshua D., Kathleen E. Powers, Brian C. Rathbun, and Ravi Iyer. 2014“Moral Support:

How Moral Values Shape Foreign Policy Attitudes.” Journal of Politics 76(3): 825-40.

Krasner, Stephen D. 2016. “International Organization 1986-91: The Rise of Norms and Domestic

Politics.” International Organization, 70th Anniversary Special Collections.

Kreps, Sarah E. 2008. “Multilateral Military Interventions: Theory and Practice.” Political Science

Quarterly 123(4): 573-603.

Koh, Harold Hongju. 1997. “Why do Nations Obey International Law?” Yale Law Journal 106(8):

2599-659.

König, Thomas and Lars Mäder. 2015. “The Strategic Nature of Compliance: An Empirical

Evaluation of Law Implementation in the Central Monitoring System of the European

Union.” American Journal of Political Science 58(1): 256-63.

Li, Xiaojun. 2010. “Social Rewards and Socialization Effects: An Alternative Explanation for the

Motivation Behind China’s Participation in International Institutions.” The Chinese

Journal of International Politics 3 (3): 347-77.

Lipscy, Phillip. 2017. Renegotiating the World Order: Institutional Change in International

Relations. New York, NY: Cambridge University Press.https://mail.google.com/mail/u/0/

- inbox

Lupia, Arthur, and Mathew D. McCubbins. 1998. The Democratic Dilemma. New York, NY:

Cambridge University Press.

Martin, Lisa. 1992. Coercive Cooperation: Explaining Multilateral Economic Sanctions.

Princeton, NJ: Princeton University Press.

March, James G. and Johan P. Olsen. 1998. “The Institutional Dynamics of International Political

Orders.” International Organization 52(4): 943-69.

Maoz, Zeev, and Bruce Russett. 1993. “Normative and Structural Causes of Democratic Peace,

1946-1986.” American Political Science Review 87(3): 624–38.

McDermott, Rose. 2009. “Psychological Approaches to Identity: Experimentation and

Application.” In Measuring Identity: A Guide for Social Scientists, edited by Rawi Abdelal,

Yoshiko M. Herrera, Alastair Iain Johnston, and Rose McDermott. New York, NY:

Cambridge University Press.

Mercer, Jonathan. 1995. “Anarchy and Identity.” International Organization 49(2): 229-52.

Milner, Helen V. and Dustin Tingley. 2016. Sailing the Water’s Edge: The Domestic Politics of

American Foreign Policy. Princeton, NJ: Princeton University Press.

Moravcsik, Andrew. 1997. “Taking Preferences Seriously: A Liberal Theory of International

Politics.” International Organization 51(4): 513-553.

Mueller, John E. 1973. War, Presidents, and Public Opinion. New York, NY: Wiley.

Press, Daryl G., Scott D. Sagan, and Benjamin A. Valentino. 2013. “Atomic Aversion:

Experimental Evidence on Taboos, Traditions, and the Non-Use of Nuclear Weapons.”

American Political Science Review 107 (1): 188-206.

Recchia, Stefano. 2015. “Soldiers, Civilians, and Multilateral Humanitarian Intervention.” Security

Studies 24 (2): 251-83.

Renshon, Jonathan. 2016. “Status Deficit and War.” International Organization 70 (3): 513-50.

Risse-Kappan, Thomas. 1991. “Public Opinion, Domestic Structures, and Foreign Policy in Liberal

Democracies.” World Politics 43(4): 479-512.

Risse-Kappan, Thomas. 1995. Cooperation among Democracies: The European Influence on U.S.

Foreign Policy. Princeton, NJ: Princeton University Press.

Risse-Kappan, Thomas. 1996. “Collective Identity in a Democratic Community.” In The Culture

of National Security: Norms and Identity in World Politics, ed. Peter J. Katzenstein. New

York, NY: Columbia University Press.

Stein, Rachel M. 2015. “War and Revenge: Explaining Conflict Initiation by Democracies.”

American Political Science Review 109 (3): 556-73.

Schultz, Kenneth. 2003. “Tying Hands and Washing Hands: The U.S. Congress and Multilateral

Humanitarian Intervention,” in Locating the Proper Authorities: The Interaction of

International Domestic Institutions, ed. Daniel Drezner. Ann Arbor, MI: University of

Michigan Press.

Sobel, Richard. 2001. The Impact of Public Opinion on U.S. Foreign Policy Since Vietnam:

Constraining the Colossus. New York, NY: Oxford Univ. Press.

Tago, Atsushi. 2005. “Determinants of Multilateralism in US Use of Force: State of Economy,

Election Cycle, and Divided Government.” Journal of Peace Research 42(5): 585-604.

Tago, Atsushi and Maki Ikeda. 2015. “An ‘A’ for Effort: Experimental Evidence on UN Security

Council Engagement and Support for US Military Action in Japan.” British Journal of

Political Science 45(2): 391-410.

Tomz, Michael. 2008. “Reputation and the Effect of International Law on Preferences and Beliefs.”

Working Paper, Stanford University. Available at:

http://web.stanford.edu/~tomz/working/Tomz-IntlLaw-2008-02-11a.pdf

Tomz, Michael, and Jessica Weeks. 2013. “Public Opinion and the Democratic Peace.” American

Political Science Review 107 (4): 849-65.

Tingley, Dustin, and Michael Tomz. 2012. “How does the UN Security Council Influence Public

Opinion?” Working paper, Stanford University. Available at:

http://web.stanford.edu/~tomz/

Thompson, Alexander. 2009. Channels of Power: The UN Security Council and U.S. Statecraft in

Iraq. Cornell, NY: Cornell University Press.

Voeten, Erik. 2001. “Outside Options and the Logic of Security Council Action.” American

Political Science Review 95 (4): 845-58.

Voeten, Erik. 2005. “The Political Origins of the UN Security Council’s Ability to Legitimize the

Use of Force.” International Organization 2005 (3): 527-57.

Weeks, Jessica L. 2008. “Autocratic Audience Cost: Regime Type and Signaling Resolve.”

International Organization 62(1): 35-64.

Wednt, Alexander. 1999. Social Theory of International Politics. Cambridge, UK: Cambridge

University Press.

Wittkopf, Eugene R. 1990. Faces of Internationalism: Public Opinion and American Foreign

Policy. Durham and London: Duke University Press.

Zaller, John. 1992. The Nature and Origins of Mass Opinion. New York, NY: Cambridge

University Press.

This Appendix supplements the paper, International Organizations and American Public Opinion

on Humanitarian War.

A Survey Description and Sample Attributes Page 1

B Questionnaires

Survey #1 2

Survey #2 5

Survey #3 7

Survey #4 8

C Historical Polls on Support for War—Case Notes 9

D Main Effects: Robustness and Extensions

Sophisticated Public and Liberal Internationalists 13

Main Effects by Target Country 14

Law Knowledge; Law Experiment 15

Conditional Effects by Beliefs about IO Conservativeness 18

E Analysis of Causal Mechanisms

Affinity and NATO Effect with Control Variable Results 20

Mediator Measurement and Coding 21

Mediation Analysis Notes 22

For this study, I fielded three original surveys. Survey #1 was fielded via YouGov, an

internet polling firm, to a nationally representative sample of 1,000 respondents. The survey was

fielded from January 7-12, 2015. Survey #2 through #4 were fielded via Amazon Mechanical Turk

(MTurk), an online service recruitment platform to a convenience samples.1 Survey #2 recruited of

408 respondents from April 29, 2016, Survey #3 recruited 1,141 respondents from February 3-4,

2016 and Survey #4 recruited 598 respondents from February 9-10.

Table A1: Survey Sample Characteristics

Attribute

Survey #1

YouGov

January 2015

Survey #2

MTurk

February

2016

Survey #3

MTurk

April 2016

Survey #4

MTurk

February

2017

Gender

Female 56% 52.4% 51.5% 58.9%

Male 43.2% 47.5% 48.5% 40.1%

Age

25 %-tile 33 Years 27 Years 26 Years 26 Years

50 %-tile 46 Years 33 Years 31 Years 31 Years

75 %-tile 60 Years 44 Years 40 Years 38 Years

Race

White 69.5% 81.8% 74.5% 71.9%

Non-White 30.5% 18.2% 26.5% 29.1%

Education

No college degree 71.4% 49.1% 50.3% 52.2%

Bachelor’s or

higher 29.6% 50.9% 49.7% 47.8%

Party Identification

Republican 25.5% 21.1% 20.3% 20.7%

Democrat 42.2% 41.2% 43.1% 43.1%

Independent/Other 32.3% 37.6% 36.5% 36.1%

1 While a convenience sample, research shows that surveys conducted via MTurk often yield findings that

are comparable to more diverse/representative studies (Berinsky, Huber, and Lenz 2012).

Programming instructions: These questions have two assigned variables: [country] and [IO]. Each

variable is assigned randomly and independently.

For [country], randomly draw an integer from 1 through 5, recorded as country.

If country = 1, then [country]= Azerbaijan

If country = 2, then [country]= Burma (Myanmar)

If country = 3, then [country]= Chad

If country = 4, then [country]= Colombia

If country = 5, then [country]= Yemen

For [IO], randomly draw an integer from 1 through 3, recorded as treatment.

If treatment = 1, then [IO] =

The United Nations Security Council passed a resolution authorizing military action to help

these civilians. China, France, Russia, the United Kingdom, and the United States voted

“yes” on the resolution.

[line break]

The North Atlantic Treaty Organization (NATO) also supports taking military action.

NATO members include France, the UK, and the US.

If treatment = 2, then [IO] =

The United Nations Security Council rejected a resolution that would have authorized

military action to help these civilians. France, the United Kingdom, and the United States

voted “yes” on the resolution, but China and Russia vetoed the resolution by voting “no.”

[line break]

Meanwhile, the North Atlantic Treaty Organization (NATO) supports taking military

action. NATO members include France, the UK, and the US.

If treatment = 3, then [IO] =

The United Nations Security Council rejected a resolution that would have authorized

military action to help these civilians. The United States voted “yes” on the resolution, but

France, China, Russia, and the United Kingdom vetoed the resolution by voting “no.”

[line break]

Meanwhile, the North Atlantic Treaty Organization (NATO) also opposes taking military

action. NATO members include France, the UK, and the US.

Question 1 of 8. SINGLE CHOICE. Support for Intervention.

Military groups fighting in [country] have killed thousands of civilians, including women

and children, and have left tens of thousands homeless and starving.

[IO]

In this situation, do you support or oppose the US sending its military to help civilians in [country]?

Support a great deal

Support a moderate amount

Support a little

Oppose a little

Oppose a moderate amount

Oppose a great deal

Question 2 of 8. SINGLE CHOICE. Reputation Mediator.

Do you think that sending the US military would improve or worsen America's reputation in other

countries?

Improve a great deal

Improve a moderate amount

Stay about the same

Worsen a moderate amount

Worsen a great deal

Question 3 of 8. SINGLE CHOICE. Casualties Mediator.

If the US sends its military, how many American lives do you think would be lost in the military

operation?

A very small amount

A small amount

A moderate amount

A large amount

A very large amount

Question 4 of 8. SINGLE CHOICE. Retaliation Mediator.

If the US sends its military, how likely do you think it is that other countries will punish the US?

Very likely

Somewhat likely

Neither likely or unlikely

Somewhat unlikely

Very unlikely

Question 5 of 8. SINGLE CHOICE. Motives Mediator.

If the US sends its military, do you think the US would be doing so for humanitarian reasons such

as protecting and delivering aid to suffering civilians, or for strategic reasons such as combating

terrorists and weakening an unfriendly government?

Completely for humanitarian reasons

Mostly for humanitarian reasons

About an equal mix of both reasons

Mostly for strategic reasons

Completely for strategic reasons

Question 6 of 8. SINGLE CHOICE. Collective Action Mediator.

If the US sends its military, how likely do you think it is that other countries would help the US

carry out the operation by contributing troops or money?

Very likely

Somewhat likely

Neither likely or unlikely

Somewhat unlikely

Very unlikely

Question 7 of 8. SINGLE CHOICE. Contagion Mediator.

If the US does not send its military, how likely do you think it is that the crisis will spread to other

countries?

Very likely

Somewhat likely

Neither likely nor unlikely

Somewhat unlikely

Very unlikely

Question 8 of 8. MULTIPLE CHOICE. International Law Knowledge.

Programming instructions: Randomly present the order of choices 1 through 4. Choice 5, “none

of the above,” will always be last.

Under international law, which of the following organizations do you think can authorize the use

of military force in another country? Pleases select all that apply.

United Nations Security Council

North Atlantic Treaty Organization (NATO)

International Court of Justice (ICJ)

Global Military Council

None of the above

Question 1 of 8. SINGLE CHOICE. Democratic Community.

People living in democratic countries that protect basic freedoms might have different customs and

cultures, but they can generally relate to one another.

Agree strongly

Agree

Neither agree nor disagree

Disagree

Disagree strongly

Questions 2 through 7 of 8. GRID: SINGLE CHOICE. Friends and Enemies.

In your opinion, do the following countries share a friendly, neutral, or hostile relationship with the

U.S.?

Rows [order is randomized]

United Kingdom

France

China

Russia

Germany

Canada

Column/Choices

Friendly

Neutral

Hostile

Question 8 of 8. SINGLE CHOICE. Support for Intervention.

Military groups fighting in [Azerbaijan OR Chad] have killed thousands of civilians, including

women and children, and have left tens of thousands homeless and starving.

[IO Treatment. Randomly and independently present one of the following four:]

The United Nations Security Council REJECTED a resolution to authorize the use of

military force to help these civilians. The United States voted “yes” on the resolution, but

France, China, Russia, and the United Kingdom vetoed the resolution by voting “no.”

Meanwhile, the North Atlantic Treaty Organization (NATO) also OPPOSES taking

military action. NATO members include the U.S., Canada, and several European countries.

The United Nations Security Council REJECTED a resolution to authorize the use of

military force to help these civilians. France, the United Kingdom, and the United States

voted “yes” on the resolution, but China and Russia vetoed the resolution by voting “no.”

Meanwhile, the North Atlantic Treaty Organization (NATO) SUPPORTS taking military

action. NATO members include the U.S., Canada, and several European countries.

The United Nations Security Council PASSED a resolution to authorize the use of military

force to help these civilians. China, Russia, and the United States voted “yes” on the

resolution, while France and the United Kingdom abstained by not voting.2 Meanwhile, the

North Atlantic Treaty Organization (NATO) OPPOSES taking military action. NATO

members include the U.S., Canada, and several European countries.

The United Nations Security Council PASSED a resolution to authorize the use of military

force to help these civilians. China, France, Russia, the United Kingdom, and the United

States voted “yes” on the resolution. Meanwhile, the North Atlantic Treaty Organization

(NATO) also SUPPORTS taking military action. NATO members include the U.S.,

Canada, and several European countries.

In this situation, do you support or oppose the U.S. sending its military to help civilians

in [Azerbaijan OR Chad]?

Support a great deal

Support a moderate amount

Support a little

Oppose a little

Oppose a moderate amount

Oppose a great deal

2 For realism, France and Britain abstained from voting rather than outright vetoing the resolution such as in

the NATO Only condition in which Russia and China veto the resolution. The trade-off for this realism is a

slightly less parsimonious experimental design. However, the design is likely to bias against the identity

theory, which predicts that NATO should matter more than the UNSC: people’s support for intervention

would likely be even lower in the UNSC Only condition if the text stated that France and Britain vetoed the

resolution.

Question 1 of 1. SINGLE CHOICE. Support for Intervention.

Military groups fighting in [Azerbaijan OR Chad] have killed thousands of civilians, including

women and children, and have left tens of thousands homeless and starving.

[IO Treatment. Randomly and independently present one of the following two:]

The United Nations Security Council REJECTED a resolution to authorize the use of

military force to help these civilians. The United States voted “yes” on the resolution, but

France, China, Russia, and the United Kingdom vetoed the resolution by voting “no.”

Meanwhile, the North Atlantic Treaty Organization (NATO) also OPPOSES taking

military action. NATO members include the U.S., Canada, and several European countries.

The United Nations Security Council REJECTED a resolution to authorize the use of

military force to help these civilians. France, the United Kingdom, and the United States

voted “yes” on the resolution, but China and Russia vetoed the resolution by voting “no.”

Meanwhile, the North Atlantic Treaty Organization (NATO) SUPPORTS taking military

action. NATO members include the U.S., Canada, and several European countries.

[information treatment. Randomly and independently present one of the following three :]

The United States is considering taking military action to help civilians in this crisis.

The United States is considering taking military action to help civilians in this crisis. To be

legal under international law, taking military action in this situation requires United

Nations Security Council authorization.

The United States is considering taking military action. Military action would save the lives

of about [80 thousand OR 620 thousand] civilians. The operation would cost the U.S.

government about [$850 million OR $4.1 billion], but the U.S. would avoid risking

casualties by not sending ground troops.

In this situation, do you support or oppose the U.S. sending its military to help civilians

in [Azerbaijan OR Chad]?

Support a great deal

Support a moderate amount

Support a little

Oppose a little

Oppose a moderate amount

Oppose a great deal

Military groups fighting in [Azerbaijan OR Chad] have killed thousands of civilians, including

women and children, and have left tens of thousands homeless and starving.

[IO Treatment. Randomly and independently present one of the following:]

The U.S., Canada, and several European countries oppose taking military action to help

these civilians.

The U.S., Canada, and several European countries support taking military action to help

these civilians.

The North Atlantic Treaty Organization (NATO) opposes taking military action to help

these civilians.

The North Atlantic Treaty Organization (NATO) supports taking military action help these

civilians.

The North Atlantic Treaty Organization (NATO) opposes taking military action to help

these civilians. NATO members include the U.S., Canada, and several European countries.

The North Atlantic Treaty Organization (NATO) supports taking military action help these

civilians. NATO members include the U.S., Canada, and several European countries.

In this situation, do you support or oppose the U.S. sending its military to help civilians

in [Azerbaijan OR Chad]?

Support a great deal

Support a moderate amount

Support a little

Oppose a little

Oppose a moderate amount

Oppose a great deal

This section provides notes for Table 1 in the main paper, which reports public opinion

during past instances in which the U.S. considered humanitarian intervention. There were often

more than one poll available for any given case. When possible, I chose polls that explicitly

mentioned a humanitarian crisis (vs “sending troops to stop a civil war”), explicitly asked about

support for military intervention (vs “what do you think about President Clinton’s handling of X

situation”), and were conducted prior to intervention. The documentation below includes my

coding notes for each case, the original survey question, and the poll citation. For reference, Table

1 is reproduced here:

Table 1 (from main paper): Past National Polls on American Support for Intervention

Cases Support Intervention? % Supporting War

UNSC NATO NATO Countries By Case Average

Rwanda 1994

Syria 2013

No

No

N/A

No

No (minus France)

No

28

33 31

Kosovo 1999

(Libya 2011)

No

(No)

Yes

(Yes)

Yes

(Yes)

53

(56)

53

(55)

Somalia 1991

Haiti 1994

Bosnia 1994

Libya 2011

Yes

Yes

Yes

Yes

N/A

N/A

Yes

Yes

Yes (Strong)

Yes (Weak)

Yes

Yes

74

34

57

56

55

Note: This table summarizes data from historical surveys conducted during episodes of potential

humanitarian intervention. NATO is coded N/A in when the case was considered “out of area” at the

time. The Rwanda poll was taken prior to France’s Operation Turquoise, which received UNSC

approval. The Libya case might be classified under “NATO Only” because the UNSC resolution

arguably did not cover the NATO airstrikes.

1. Rwanda 1994

a. Notes: The classic example of the world standing idly by as genocide unfolded.

While France was pro-intervention, most of the other western democracies could

not settle on committing to taking action. If anything the U.S. was directly

impeding efforts to declare a genocide and intervene. Support for intervention was

incredibly low (28%), though the big confounder here is that Americans were still

reeling in from the Black Hawk incident in Somalia.

b. Q: In order to stop the killing in Rwanda, do you favor or oppose the United States

sending in ground troops?

c. Ref: CBS News. CBS News Poll, Jun, 1994 [survey question].

USCBS.94JN23.R31. CBS News [producer]. Cornell University, Ithaca, NY:

Roper Center for Public Opinion Research, iPOLL [distributor], accessed Mar-10-

2017.

2. Syria 2013

a. Notes: President Obama made quite an earnest stance to take military action for

the gross violations of international humanitarian law—Syria’s use of chemical

weapons against civilians amidst civil war. However key allies in NATO like

Britain and France back-peddled from backing the U.S., and Russia was blocking

any resolution that would authorize war. Note that the Syria poll asked whether

people supported different forms of the use of force (e.g. air strikes, ground troops,

etc), but I aggregated all support for any form of military action into one value.

b. Q: As you may know the Obama Administration has concluded that the

government of Syria used chemical weapons, including nerve gas, to kill over

1,400 civilians last month. Which of the following best describes what you think

the U.S. should do in response? Do nothing and stay out of the Syrian civil war.

Launch a LIMITED military strike, using only air power, to punish the Syrian

government for using chemical weapons. Launch a MORE SUSTAINED military

strike, using only air power, to help rebels overthrow the Syrian government.

Launch a FULL-SCALE military strike, including both air power and U.S. ground

troops, to help rebels overthrow the Syrian government. [NOTE: The table

aggregates people’s support for any type of military operation compared to “do

nothing and stay out.”]

c. Ref: United Technologies/National Journal. United Technologies/National Journal

Congressional Connection Poll: Syria, Sep, 2013 [dataset]. USNJCC2013-33836,

Version 2. Princeton Survey Research Associates International [producer]. Storrs,

CT:Roper Center for Public Opinion Research, RoperExpress [distributor],

accessed Feb-22-2016.

3. Kosovo 1999

a. Notes: The UNSC would not authorize military intervention (due to Russia’s veto

threat), but NATO’s North Atlantic Council authorized war instead.

b. Q: Next we have a few questions about the situation in the Kosovo region of

Yugoslavia -- the area that has been in the news recently. As you may know, last

week, the military alliance of Western countries called NATO launched air and

missile attacks against Serbian military targets in Yugoslavia. Do you favor or

oppose the United States being a part of that military action?

c. Ref: CNN/USA Today. Gallup/CNN/USA Today # 9903019: Kosovo, Mar, 1999

[dataset]. USAIPOCNUS1999-9903019, Version . Gallup Organization

[producer]. Storrs, CT:Roper Center for Public Opinion Research,

RoperExpress [distributor], accessed Feb-22-2016.

4. Libya 2011

a. Notes: The UNSC passed a Chapter VII resolution to protect civilians, but many

including Russia argue that the resolution did not cover NATO’s airstrikes that in

effect aided rebels in overthrowing Qaddafi.

b. Q: A coalition of international forces has been enforcing a no-fly zone over Libya,

and attacking Libyan forces when they're believed to be threatening civilians. Do

you support or oppose the participation of U.S. military aircraft in this effort? c. Ref: ABC News / The Washington Post. ABC News/Washington Post Poll: June

Monthly--Federal Budget Deficit/War on Terrorism/2012 Presidential Election,

Jun, 2011 [dataset]. USABCWASH2011-1124, Version 2. Langer Research

Associates/TNS Intersearch [producer]. Storrs, CT:Roper Center for Public

Opinion Research, RoperExpress [distributor], accessed Feb-22-2016.

5. Somalia 1991

a. Notes: The UNSC passed a Chapter VII resolution to allow the use of military

force to save lives. NATO was not considering out of area operations at the time,

so is coded N/A.3 However, the entire democratic community voting in the UNSC

voted for intervention. Also, several additional others directly participated in the

intervention itself. This was a clear case of the world taking a concerted effort to

launch a humanitarian intervention. The anomalously high levels of support

probably in part reflects the rosy eyed view Americans had about their country’s

first real humanitarian intervention after the successful Cold War and First Gulf

War.

b. Q: Do you approve or disapprove of the decision to send U.S. (United States)

armed forces into the African nation of Somalia as part of a United Nations effort

to deliver relief supplies there?

c. Ref: Gallup Organization. Gallup Poll, Dec, 1992 [survey question].

USGALLUP.121192.R1. Gallup Organization [producer]. Cornell University,

Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor],

accessed Mar-10-2017.

6. Haiti 1993

a. Notes: Despite having UNSC, this intervention received fairly low levels of public

support. Again, NATO did not consider this out of area case. The democratic

community showed weak support for this intervention: Operation Uphold

Democracy in Haiti was really primarily a U.S. affair rather than a policy whole-

heartedly adopted by any multilateral group of countries. This stylized fact was

understood by the U.S. public. Indeed, when asked “When U.S. (United States)

troops went into Haiti, did you think of it primarily as a U.S. or a U.N. (United

Nations) operation?” 71% of Americans replied “U.S.” and only 24 % replied “UN

Operation.”4

b. Q: Do you approve or disapprove of the U.S. (United States) troops in Haiti?

3 That is, NATO in the 1990s only considered missions in Europe. Through the 2000s it began expanding

its operations to the MENA region and beyond. 4 Program on International Policy Attitudes, University of Maryland. United Nations Peacekeeping Survey,

Apr, 1995 [survey question]. USUMARY.95UNO.R45. Program on International Policy Attitudes,

University of Maryland [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion

Research, iPOLL [distributor], accessed Mar-10-2017.

c. Ref: Program on International Policy Attitudes, University of Maryland. United

Nations Peacekeeping Survey, Apr, 1995 [survey question].

USUMARY.95UNO.R45. Program on International Policy Attitudes, University

of Maryland [producer]. Cornell University, Ithaca, NY: Roper Center for Public

Opinion Research, iPOLL [distributor], accessed Mar-10-2017.

7. Bosnia 1994

a. Notes: In Bosnia, both the UNSC and NATO pretty clearly supported the use of

force.

b. Q: Would you support or oppose the United States, along with its allies in Europe,

carrying out air strikes against Bosnian Serb forces who are attacking the Bosnian

capital of Sarajevo?

c. Ref: ABC News. ABC News Poll: Bosnia Attack Poll, Feb, 1994 [dataset].

USABC1994-5174, Version 2. ABC News [producer]. Storrs, CT:Roper Center

for Public Opinion Research, RoperExpress [distributor], accessed Feb-22-2016.

Here, I estimate the effect of IOs among the sophisticated public and liberal

internationalists, two subgroups that are thought to be particularly influential to foreign policy.

Here, sophisticated respondents are over 35 years old, college educated, frequent followers of

international politics, and registered voters. Liberal internationalists are ideologically liberal and

believe that the U.S. should “take an active part in world affairs.” Figure A1 gives the results of

this analysis. Overall, sophisticated and liberal internationalist audiences follow a pattern similar

to the general public in their responsiveness to IO endorsements: NATO significantly boosts their

support for intervention, but an additional UNSC endorsement does not.

Figure A1: The Effect of IOs among the Sophisticated Public and

Liberal Internationalists

Note: This figure shows the proportion of respondents supporting intervention for

each experimental group among the sophisticated public and liberal

internationalists. “None” indicates an endorsement from neither NATO nor the

UNSC. “NATO” is an endorsement from only NATO. “Both” is an endorsement

from both IOs. The sophisticated public is at least 35 years old, college educated,

follow the news about international politics on a daily basis, and are registered

to vote (N=169). Liberal internationalists report liberal political ideology and

believe that the U.S. should take an active role in foreign affairs (N=180). 95%

confidence intervals are given. Data are from Survey #1.

Figure A2 below shows the main treatment effects conditional on the target country of

military intervention. The five countries were independently randomized in the vignette. Overall,

the results show that none of the conditional treatment effects are significantly distinguishable from

the average treatment effect (dotted line) or the treatment effect aggregating across all countries.

Figure A2: The Effect of IOs Conditional on Country Country

Note: This figure shows the effect of IOs on support for armed intervention, conditional on the target

country of intervention. “None” indicates an endorsement from neither NATO nor the UNSC. The

dotted line indicates the average treatment effect, or the aggregate effect across all countries.

“NATO” is an endorsement from only NATO. “Both” is an endorsement from both IOs. 95%

confidence intervals are reported in brackets. N=1,000. Data are from Survey #1.

The legal arguments imply two critical hypotheses about the effects of IOs. First, knowledge about

international law moderates the effects of IOs: among those who know international law, NATO’s

endorsement effect on Support should be smaller and the UNSC’s effect should be larger. Second,

explicit legal criteria should diminish the effect of NATO: when respondents are directly told that

interventional legally requires UNSC authorization, they should be less swayed by NATO.

To test the knowledge hypothesis, I first measure whether respondents know international

law. Respondents read, “Under international law, which of the following organizations do you think

can authorize the use of military force in another country? Pleases select all that apply.” The

possible choices are: the United Nations Security Council, NATO, International Court of Justice,

Global Military Council (a “placebo” answer), and None of the above. These choices are presented

in a random order, except for “None of the above,” which is always last. Respondent who select

the UNSC and no other choices are coded as knowing international law (Know Law), while all

others are not (Don’t Know Law). Contrary to the law hypothesis, Figure A3 illustrates that the

main effect of IOs is virtually identical regardless of whether or not respondents know the law.

Some people might have legal knowledge, but they do not tap into that knowledge as a criterion

for evaluating their opinions about intervention.

Figure A3: Prior Knowledge of International Law Does Not Change How IOs

Affect Support for Intervention

Note: Using probit coefficient estimates, this figure shows the predicted probability of

supporting intervention for each treatment group, conditional on whether respondents

know international law (N=237) or do not (N=763). “None” indicates an endorsement

from neither NATO nor the UNSC. “NATO” is an endorsement from only NATO. “Both”

is an endorsement from both IOs. It also shows the marginal effect of knowing the law or

the “law difference.” Those who “know law” correctly identified the UNSC as the sole IO

that can authorize armed interventions. 95% confidence intervals are given. Data are from

Survey #1.

To test the legal criteria hypothesis, I conducted an additional survey in which I

independently randomize (1) whether respondents receive the None or the NATO Only scenario,

and (2) whether or not respondents receive an explicit statement about legal requirements (i.e. a

2X2 factorial design). All respondents read: “The United States is considering taking military

action to help civilians in this crisis.” Respondents in the law group additionally read: “To be legal

under international law, taking military action in this situation requires United Nations Security

Council authorization.” Figure A4 shows the results from these experiments: directly informing

respondents about the law does not diminish NATO’s influence on mass opinion. Whether or not

respondents are given the legal criteria, the effect of NATO’s endorsement is about 30 points.

Figure A4: Being Told that UNSC Approval is Legally Required for

Intervention Does Not Diminish NATO’s Effect on Public Opinion

Note: Using probit coefficient estimates, this figure shows the predicted probability of

supporting intervention for each IO treatment group, conditional on whether or not

respondents were given information about the legal requirements for humanitarian

intervention. “None” indicates an endorsement from neither NATO nor the UNSC.

“NATO” is an endorsement from only NATO. The figure also shows the “law difference,”

the effect of the legal information experiment. 95% confidence intervals are given. Data

are from Survey #3.

Turning to the information theory, a critical implication is that people’s beliefs about an

IO’s membership affects the ability of that IO to relay influential information to citizens. In

particular, the more conservative an IO in its support for war, the greater effect that IO should have

on public opinion. This argument further states that conservativeness is measured using the IO’s

pivotal member’s ideological distance from the cue-receiver (Chapman 2011). To test this

hypothesis, I return to Survey #2, which records citizen support for intervention for all four

experimental groups (None, UNSC Only, NATO Only, Both). With this, I estimate the average effect

of each IO conditional on respondents’ beliefs about the IO’s ideological distance. To measure

perceptions of ideological distance, respondents shared their opinions about whether the following

six veto-holding member countries “share a friendly, neutral, or hostile relationship with the U.S.”:

Canada, China, Germany, France, Russia, and the United Kingdom.5

With this data, I create a “pivotal member score” for each respondent’s view of each IO.

For NATO, the pivotal member score is the most hostile response given from the countries Canada,

Germany, France, and the United Kingdom. For example, if a respondent believed that Canada,

Germany, and the UK were “friendly” and France was “neutral,” then the distance score would be

“neutral.” For the UNSC, the score is calculated using the responses for China, France, Russia, and

the United Kingdom. With this data, I then split the sample at approximately its median distance

score for each IO, creating a binary measure of IO pivotal member distance. This creates two subset

of respondents for each IO: those who perceive the IO’s pivotal member as relatively close versus

relatively far.

Table A5 reports the NATO and UNSC effects conditional on whether respondents believe

each IO’s most distant member is far or close. Opposite of what the information theory predicts,

the IO effects are largest among those who perceive the pivotal member to be closest. Among those

who perceive NATO’s pivotal member to be close, NATO has a 22.6 point effect on Support. But

among those who perceive that member to be far, NATO only has a 6.9 point effect. Similarly, the

UNSC’s effect is largest among those who perceive its pivotal member to be far (10.5 point effect)

5 China, France, Russia, and the UK hold a veto on the UNSC. Canada, France, Germany, and the UK are

pivotal members on the North Atlantic Council of NATO, which is a consensus decision-making body.

as opposed to being close (2.7 point effect). These results contradict the information theory’s main

hypothesis.

Table A5: Perceptions of IO Membership and

the Effect of IOs

IO

IO endorsement

effect on Support

(in % points)

NATO’s pivotal

member is

ideologically…

Close to the U.S.

N=232

22.6*

Far from the U.S.

N=176

6.9

UNSC’s pivotal member

is ideologically…

Close to the U.S.

N=160

10.5

Far from the U.S.

N=248

2.7

Note: For various groups, this table reports the effect

of an IO endorsement on support for intervention.

Asterisks denote effects that are significant at the 0.05

level. Data are from Survey #2.

Affinity and NATO Effect with Control Variable Results

Figure A5 presents the exact same analysis in Figure 3 in the main paper except now with

the control variables that were originally not displayed.

Figure A5: NATO’s Effect is Strongest among Americans who Identify with NATO’s

Members (With Control Variables)

Note: This figure reports the marginal predicted probabilities from probit coefficients of various

explanatory factors of people’s intervention support. The outcome takes a value of 0 if the respondent

opposes intervention, and a value of 1 if the respondent supports intervention. The baseline category is

the condition in which NATO opposes intervention and respondents express low affinity toward NATO’s

members. Control variables (gender, age, education, party ID, and ideology) are reported in Appendix

E. 95% confidence intervals are given. N=408. Data are from Survey #2

.054

-.0009

.19

.01

-.002

-.13

-.014

-.028

.014

NATO

Affinity

NATO*Affinity

Education

Age

Female

White

Republican

Conservative

-.4 -.3 -.2 -.1 0 .1 .2Change in Probability of Supporting Intervention

Table A6: Measurement of Mediators

Mediator Measurement Values

Reputation*

Do you think that sending the US military

would improve or worsen America's

reputation in other countries?

= 1 if else;

0 if “worsen”.

Collective

Action

If the US sends its military, how likely do

you think it is that other countries would

help the US carry out the operation by

contributing troops or money?

= 1 if “likely”;

0 if else.

Humanitarian

Motives

If the US sends its military, do you think the

US would be doing so for humanitarian

reasons such as protecting and delivering aid

to suffering civilians, or for strategic

reasons such as combating terrorists and

weakening an unfriendly government?

= 1 if “mostly

humanitarian”;

0 if else.

Prevent

Contagion

If the US does not send its military,

how likely do you think it is that the

crisis will spread to other countries?

= 1 if “likely”;

0 if else.

Retaliation

Unlikely*

If the US sends its military, how

likely do you think it is that other

countries will punish the US?

= 1 if else;

0 if “likely”.

Casualties

Unlikely*

If the US sends its military, how many

American lives do you think would be lost

in the military operation?

= 1 if else;

0 if “large amount”.

Note: These questions are from Survey #1. Asterisks indicate questions that were asked in the

reverse. Asking questions in such a way helps to avoid creating artificial correlation among the

responses. But for the analysis, I present the results in the “positive” form (i.e. a greater value

corresponds with what most would associate with greater support for intervention).

This section gives a more technical discussion of “Test #2 Directly Estimate Social Mechanisms”

of the main paper. The mediation analysis process obtains the predicted values of the mediator and

dependent variable by fitting parametric models on the observed data, and then iterates this process

to estimates the average mediation effects. I apply probit models because the mediator and outcome

variables are binary. Identifying the mediation effects require meeting the sequential ignorability

assumption—that assignment to treatment and mediators are as if random (Imai et al. 2011, 770).

For the mediators to be “as if random” they must be uncorrelated with any omitted variables and

independent from one another. In the analysis presented in the paper, I address the issue of omitted

variables by including control variables when estimating the effect of each mediator.

I begin the analysis by assuming that the causal mediators are statistically independent,

which is common in recent studies that employ mediation analysis (e.g. Tomz and Weeks 2013).

However, I do argue that the identity mechanisms (collective action, reputation, and motives) are

part of the same social process, and thus they are likely to impact each other. If I relax the

independence assumption, I can no longer identify the distinct effect of any particular mechanism,

but can still infer that some combination of them are significant. Yet still, another concern is that

Contagion confounds the entire set of social mechanisms. I address this by estimating the mediation

effects of the social mechanisms conditional on Contagion taking a value of zero (i.e. the

respondents among which the Contagion variable remains untapped). Table A7 give the results.

The substantive results remain, and if anything the importance of reputation increases.

Table A7: Mediation Analysis Conditional on

Contagion Mediator

Mediator

Mediation Effect

Full Sample When

Contagion = 0

Collective Action 6.4 6.5

Reputation 3.9 6.6

Humanitarian 1.5 1.5