My research demonstrates how political opinion, psychology, and norms influence the domestic politics of democracy and war. These two clusters of research, on democracy and on war, have generated distinct implications for understanding cooperation and conflict in international relations.


1. Democracy
Insight: democracy and democratic norms have become widespread within societies but continue to create social division between different countries.

Over the last century, the world has converged around liberal and especially electoral democracy as a way to organize political society. The number of democratically governed countries has increased rapidly over this time period, and just as importantly, the number of autocratic governments that adopt democratic institutions, such as elections and multiparty systems, has also flourished (Magaloni, Chu, and Min 2013). People living under both democratic and nondemocratic governments embrace democratic norms in punishing undemocratic leaders who act unilaterally in the domestic and foreign policymaking process (Chu and Williamson 2024). People from a range of cultures also define “democracy” in terms of elections and civil liberties, against increasing attempts to re-define democracy by authoritarian powers (Chu, Williamson, and Yeung 2024). 

However, when it comes to international relations, democracy and especially liberal democracy fail to consistently bring different societies together. Instead, liberal democratic countries form an exclusive social group or "club." This group’s shared values help to sustain domestic support for its military alliances (Chu, Ko, and Liu 2021). The social affinity among democracies also explains why organizations like NATO, which represents the liberal community, can influence the foreign policy preferences of citizens and policymakers within the democratic ingroup (Chu w.p.). 

This democratic social identity in international politics is not limited building ingroup cohesion. It also generates friction with outgroups. Citizens of liberal democracies, for example, judge autocratic powers as threats to the international system, even when accounting for traditional economic and security factors (Chu 2021). Similarly, policymakers of liberal democracies discriminate against economic investment originating from autocratic countries, and such discrimination is distinctly due to political regime and ideology, rather than other factors like race (Chu w.p.; Chen and Chu w.p.).

Thus, the cleavage between democracies and nondemocracies has been deeply embedded into how citizens and elites alike think about international relations. The impact on elites matters because elites make policy. The impact on the mass public also matters because public opinion influences policymaking in democratic countries (Chu and Recchia 2022), and citizen biases or outright discrimination can also influence everyday interactions in cosmopolitan societies like the United States.
2. Warfare
Insight: despite major advances in international law and the regulation of warfare, people’s more deeply held norms, values, and psychological traits continue to inform their thinking on warfare.

One of human society’s major accomplishments in the 20th century was to enshrine customs of war into nearly universally accepted international law and institutions, such as the Geneva Conventions. Optimists argue that such legalization influences people to internalize deeper commitments to morality regarding war.

This achievement should be celebrated, but a closer look at how these laws and institutions interact with human psychology and people’s beliefs raises some doubts. There are several examples of this complex relationship that ultimately show how international law's impact is limited by people's pre-existing values.

First, international law is supposed to unconditionally ban certain types of wartime conduct, such as the abuse of prisoners of war. People, however, deeply held commitments to the principle of reciprocity remains: they still largely support reciprocal wartime abuses and are only willing to abide by international law when other countries also commit to do the same (Chu 2019). Relatedly, international law bans all wars except for those fought in self-defense or that are endorsed by the UN Security Council. However, international approval of war still follows a more deeply engrained moral and social-psychological logic: people approve of illegal wars that pursue humanitarian aims, and when deciding whether to wage war, they care more about receiving the endorsement of their social peers than legalizing or universalistic institutions like the Security Council (Chu w.p.).

Second, international legal doctrine broadly states that we must evaluate people’s intentions in order to judge whether their wartime actions are justified. For example, the law distinguishes intentionally versus accidentally bombing a hospital. But people’s psychological predispositions lead them to, instead, first react to the moral harm created by an action, and then draw conclusions about intentions: if an action created harm, they tend to assume it was done intentionally. When something bad happens, people have a bias to assume its a purposeful conspiracy (Chu, Holmes, and Traven 2020; Traven, Holmes, and Chu 2023).

Third, people’s attitudes toward war continue to be significantly shaped by their social identity. Humanitarian wars, for example, should in theory be waged to save innocent civilians without discrimination, but people are more likely to support such interventions to save civilians with whom they identify, especially along religious dimensions (Chu and Lee 2024). Similarly, even policymakers express identity biases in their receptivity to refugees (Shaffer, Pinson, Chu, and Simmons 2020), which are supposed to be received based on universal humanitarian standards rather than identity. People’s support for post-war reconciliation, such as having their government apologize for war crimes, are also greatly shaped by nationalism or their identity attachment to their nation (Kitagawa and Chu 2021).

So ultimately, while the international community has come a long way in legalizing and universalizing ethical standards in warfare, people still hold onto their more basic psychological and social psychological instincts, even when they are directly informed about international standards. What might be more disturbing is that in some cases, people may know what the international norms and laws are, but hide their true beliefs and support for illegal conduct, such as using chemical weapons during warfare (Blair, Chu, and Schwartz 2022). So human society still has a long way to go in internalizing the aspirations that international law sets in the realm of war.