The development of nuclear weapons added a new dimension to conventional conflict: the possibility that it could inadvertently escalate into a nuclear exchange. How does this relationship between conventional war and nuclear escalation shape deterrence? I present a formal model of deterrence and arming. The novelty here is that investing in conventional capabilities has a direct effect on the balance of power but also an indirect effect on conflict duration and the likelihood of an accidental nuclear exchange. I find that accounting for the risk of nuclear escalation may require greater conventional force postures for deterrence, thus lowering welfare in the absence of nuclear war. I also find the nuclear era will be more peaceful, but when conflicts occur, they may be more aggressive and decisive. These results (and others) offer insight into the difficulty of substituting nuclear weapons for conventional arms, and into the Soviet response to the 1956 Hungarian Revolution.

How does power affect threat perception? Drawing on advances in psychological research on power, I find that the sense of state power inflates the perception of threats. The sense of power activates intuitive thinking in the decision-making process, including a reliance on gut feelings and cognitive shortcuts like heuristics and prior beliefs. In turn, as psychological IR research shows, these mechanisms tend to inflate threat perception. The powerful assess threats from the gut rather than the head. Experimental evidence from the US and China, a reanalysis of a survey of Russian elites, and a large-scale text analysis of Cold War US foreign policy elites lend support to this expectation. The findings help to psychologically reconcile enduring theoretical puzzles—from “underbalancing” to “overextension”—and generate entirely new ones, like the possibility that decision makers of rising, not declining, states feel more fear. Together, the paper offers a “first image reversed” challenge to bottom-up accounts of psychological IR. Decision-maker psychology is also a dependent variable shaped by the balance of power, with important implications for a world returning to great power competition.

Under what conditions do insurgents challenge gender norms in the midst of conflict? And what do they gain by doing so? Using an original data set of 137 armed groups fighting between 1950 and 2019, I argue that armed groups challenge gender customs to reshape local power relations. With 40 percent of rebel groups regulating civilian gender customs during civil war, this strategy is remarkably widespread, comparable to taxation or the provision of basic security in its prevalence. I demonstrate that armed groups exploit pre-existing gender grievances, using strategies like punishing domestic violence (9 percent of groups), banning dowries (15 percent), and enforcing dress codes (11 percent) to empower targeted subsections of the population and undermine local elites. I combine cross-national analysis with qualitative case studies of al-Qaeda in the Islamic Maghreb and Katiba Macina, two Islamist groups in Mali. This allows me to demonstrate how the approach to local elites drives gender governance in two groups with a shared ideology, goals, and societal context.

When is science politicized in the international climate change regime? Does greater scientific certainty protect it from becoming politically contentious? I study these questions in the context of the Intergovernmental Panel on Climate Change (IPCC), the organization responsible for communicating the global scientific consensus on climate change. Using newly digitized data from inter-state negotiations at the IPCC, I show that states attempt to influence the IPCC’s assessment of scientific consensus in line with their bargaining positions in climate change negotiations. Estimating an ideal-point model, I find that the predominant cleavage over climate science is distributional—between new and old industrializers with broader ideological disagreements, rather than between large polluters and vulnerable countries. Next, I show that this cleavage is mediated by scientific uncertainty. Large polluters are more likely to agree with each other on interpretations of relatively uncertain science, which allows them to jointly weaken the scientific basis for strong climate agreements. Conversely, these countries are less likely to agree on relatively certain science, which heightens conflict over the distribution of the burden of mitigation. Thus greater scientific certainty may change the nature of politicization rather than reducing it.

Climate treaties have progressed over time to pledge substantial reductions in global warming. This is surprising, given that theories of climate politics emphasize collective-action problems and domestic deadlock. I first describe the process of updating climate mitigation targets under the Paris Agreement. Then I develop a theoretical argument that explains target changes based on how countries are situated in economic and political networks. Trade flows create competitive economic pressures that may undermine climate action, but these pressures may ebb when partners also commit to act. I argue that political networks support conditional cooperation, especially when institutional design promotes gradual commitments. I use spatial regression models to study how countries’ climate targets are related to their partners’ prior targets. I find that countries pledged stronger updated mitigation targets in the Glasgow Climate Pact when their closest political partners submitted strong targets in the Paris Agreement. This suggests the Paris Agreement drove conditional cooperation on mitigation.

We introduce a dynamic game of outbidding where two groups use violence to compete in a tug-of-war fashion for evolving public support. We fit the model to the canonical outbidding rivalry between Hamas and Fatah using newly collected data on Palestinian public support for these groups. Competition has heterogeneous effects, and we demonstrate that intergroup competition can discourage violence. Competition from Hamas leads Fatah to use more terrorism than it would in a world where Hamas abstains from terrorism, but competition from Fatah can lead Hamas to attack less than it otherwise would. Likewise, making Hamas more capable or interested in competing increases overall violence, but making Fatah more capable or interested discourages violence on both sides. These discouragement effects of competition on violence emerge through an asymmetric contest, in which we find that Fatah uses terrorism more effectively to boost its support, although Hamas has lower attack costs. Expanding on these results, we demonstrate that outbidding theory is consistent with a positive, negative, or null relationship between measures of violence and incentives to compete.

We use a formal model to explore leaders’ incentives to set climate commitments and subsequently exert downstream mitigation effort. Since the Paris Agreement asks countries to make unilateral voluntary commitments, we investigate the domestic factors motivating climate pledges. We study a country with electoral competition between two parties, Green and Brown, who first make commitments to reduce emissions and then implement policies to meet their commitments. Voters anticipate the equilibrium policies each party will implement given the pledge. If downstream mitigation policies are insufficient relative to the commitment, the government is “shamed” by the international community. Several incentive channels arise when parties make commitments, as they have policy and electoral value. Parties can use commitments to tie the opposition’s hands to implement preferential policies in the future. If parties care only about winning elections, they will exploit commitments to serve electoral needs, which paradoxically leads anti-environmental parties to implement more ambitious commitments.

Thomas Schelling argued that “The most spectacular event of the past half century is one that did not occur. We have enjoyed sixty years without nuclear weapons exploded in anger.” To this, he added a question: “Can we make it through another half dozen decades?” Contemporary technological innovation, weapons proliferation, increased modernization efforts, and nuclear saber-rattling have made Schelling's question an urgent one. Recently, there has been an explosion in scholarship attempting to test the resilience of nonuse. These scholars have focused primarily on methodological innovations, generating an impressive body of evidence about the future of nonuse. Yet we argue that this literature is theoretically problematic: it reduces mechanisms of nuclear nonuse to a “rationalist” versus “normative” dichotomy which obscures the distinct pathways to nuclear (non)use within each theoretical framework. With rationalist theories, the current literature commits the sin of conflation, treating what should be distinct mechanisms—cost and credibility—as a single causal story. With normative theories, scholars have committed a sin of omission, treating norms as structural and overlooking mechanisms of norm contestation. We show that teasing out these different causal pathways reveals radically different expectations about the future of nonuse, especially in a world of precision nuclear weapons.

Can states improve their international image by apologizing for past wrongs, or do apologies hurt countries’ reputations? We argue that apologizing can boost a country’s international image by providing reassurance about future behavior and conveying appropriate values. Yet apologies could also signal weakness, and their international effects could depend on reactions in the sending and receiving countries. To test these arguments, we pair large-scale US-based survey experiments involving Russia’s invasion of Ukraine with the historical case of Germany’s 1951 Holocaust apology. In our experiments, respondents learned whether a foreign state apologized for past offenses, how the target of the apology responded, whether key domestic groups in the sender opposed the apology, and whether the sender was democratic or not. We found that apologies boosted foreign favorability and willingness to cooperate, and did not indicate weakness. These effects persisted even if the target rejected the apology or the apology provoked backlash inside the sender, and did not depend on whether the sender was described as democratic. The case of Germany’s 1951 Holocaust apology corroborates these patterns. Together, our findings suggest that apologies may be a powerful tool of public diplomacy.

Experts argue that resource transfers from developed to developing countries are central to international climate policy efforts. Yet as countries grapple with the political difficulties of provisioning and accepting climate funds, understanding why voters support or oppose international climate finance becomes critical. Focusing on domestic audiences in both donor and recipient countries, we investigate the determinants of public support for cross-border climate transfers. Theoretically, we focus on the effects of emphasizing the compensatory purposes of funding, favoring mitigation over adaptation activities, and prioritizing partnerships between donor and recipient agents—three factors that generate both normative and material benefits, and thus build support among broader coalitions of voters. Paired survey experiments in the United States and India corroborate the relevance of these transfer features for citizens in donor and recipient countries. Taken together, our findings shed light on the domestic political-economy attributes of transfer agreements that can unlock support for cross-border climate cooperation.

Armies sometimes use fratricidal coercion—violence and intimidation against their own troops—to force reluctant soldiers to fight. How this practice affects battlefield performance remains an open question. We study fratricidal coercion using a mixed-methods strategy, drawing on (1) monthly panel data on Soviet Rifle Divisions in World War II, built from millions of declassified personnel files; (2) paired comparisons of Rifle Divisions at the Battle of Leningrad; and (3) cross-national data on 526 land battles and war outcomes from 75 conflicts (1939–2011) to assess generalizability. We offer three sets of empirical findings. First, coercion keeps some soldiers from fleeing the battlefield, but at the cost of higher casualties and reduced initiative. Second, wartime and prewar coercion (such as mass repression and officer purges) affect soldiers’ behavior in similar, mutually reinforcing ways. Third, the resolve-boosting, initiative-dampening effects of fratricidal coercion generalize across belligerents and wars. Fratricidal coercion generates compliance through fear, compelling soldiers with variable levels of resolve to conform to a uniform standard of battlefield behavior. But the net utility of this approach is dubious. On balance, countries employing fratricidal coercion are less likely to win wars.

The legitimacy of armed forces in the eyes of civilians is increasingly recognized as crucial not only for battlefield effectiveness but also for conflict resolution and peace building. However, the concept of “military legitimacy” remains under-theorized and its determinants poorly understood. We argue that perceptions of military legitimacy are shaped by two key dimensions of warfare: just cause and just conduct. Leveraging naturally occurring variation during one of the deadliest urban battles in recent history—the multinational campaign to defeat the Islamic State in Mosul, Iraq—we evaluate our theory using a mixed-methods design that combines original survey data, satellite imagery, and interviews. Civilians living in neighborhoods where armed forces were less careful to protect civilians view those forces as less legitimate than civilians elsewhere. Surprisingly, these results persist after conditioning on personal experiences of harm, suggesting that perceptions are influenced not only by victimization—consistent with previous studies—but also by beliefs about the morality of armed forces’ conduct and the cause for which they are fighting.

While recent research on the origins of proportional representation (PR) in Europe has focused on domestic political explanations, we bring international trade back as an economic explanation for the politics of electoral system choice. Spurred by Rogowski’s (1987) theory of the trade origins of PR and the political economy literature on trade policy, we argue that political conflict over trade shaped the struggle over electoral reform during the first globalization. Because tariffs were a central and contested issue, economic interests hurt by rising tariffs under the old electoral system had economic motives to support the introduction of PR. To test this theory, we leverage district-level popular votes in Switzerland using a within-country research design. We find support for the core mechanism of the trade theory: demand for protectionism entailed stronger opposition to the introduction of PR. Using panel data, we demonstrate that changes in the relative size of the agricultural sector, the central pillar of support for protectionism, were closely related to changes in support for PR. We also examine legislative voting in Germany and find that protectionism was linked to subsequent opposition to electoral reform. Altogether, our analysis highlights the neglected importance of trade in conflict over electoral institutions.