Research
Refereed Journal Articles
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Scott Wolford and Yuji Masumura. Forthcoming. Shifting Power, Interstate War, and Domestic Politics. American Journal of Political Science. Article
Abstract
We analyze a model in which shifting power undermines rising foreign states' commitments to the status quo, and domestic leaders can't credibly communicate the scale of averted power shifts after preventive war. Domestic publics prefer war only when power shifts are large, but preventive war leaves them unobservable, giving leaders incentives to lie ex post to avoid political punishment. When publics are ex ante skeptical over the value of prevention and war outcomes are middling, the probabilities of war and political punishment, as well as public skepticism over the value of war, all increase in war outcomes. We show that public strategies of punishing military failures are uniquely unsuccessful at discouraging undesirable preventive war, and the same conditions that encourage preventive war undermine its political benefits. We also use the model to explain why Japan's leaders failed to convince the public of preventive success against Russia in 1905.
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Yuji Masumura and Atsushi Tago. 2023. Micro-foundations of the Quest for Status: Testing Self-Status Perception and the Multilateral Use of Force, Foreign Policy Analysis. Article, Appendix, Data
Abstract
Research on status in international relations has expanded in the last few decades. The key empirical studies suggest that status concern generates an incentive for initiating international conflicts since unilateral military engagement is believed to increase the status of a country. We concur with this argument. However, a further study should be conducted to find if "multilateral" military engagement can change status perceptions and therefore be related to international politics over status. The test is important since the multilateral use of force is distinct from the unilateral use of force in its theoretical background and its connotation in world politics. In our experiment conducted in Japan, we treat the information on the multilateral use of force, and examine whether variations of the treatment information change people's perception over their country's international status. The results show that participation in a multilateral use of force increases and an early departure from the multilateral mission out of casualty concerns decreases their country's status perception. Also, we successfully identify that the people who have a high social dominance orientation (SDO) trait are more susceptible to such information.
Working Papers
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Arming, Alliance, and Screening. Presented at ISA 2025. slide
Abstract
I develop a formal model in which a rising state's arms buildup creates an incentive for preventive war due to the fear of hidden revisionism. I then examine how alliances alter this strategic interaction. The model reveals a screening effect: alliances make arms buildup more informative by changing its value and purpose, and this screens the otherwise hidden intention of a rising protégé. This mechanism solves a different information problem from existing theories, and fully committed alliances can simultaneously deter aggression and restrain a protégé. Two historical cases, German reaction in the July Crisis and Japanese military politics after WWII, illustrate the model's usefulness. A large-N analysis further supports the theory, showing that alliances decrease the likelihood of preventive war.
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A Theory of Cost-Sharing Renegotiations in Military Alliances. Presented at APSA 2024 and Texas Triangle 2025. (Under Review)
Abstract
The literature on military alliances suggests that alliances can deter aggression through costly signaling. In reality, however, protégés often share substantial alliance costs, which makes alliances cheaper for their patron and undermines the signal. Why do protégés do that? To explain this puzzle, I develop a formal model in which allies renegotiate their cost-sharing under the shadow of an international crisis and domestic politics. The model identifies two mechanisms by which cost-sharing renegotiations sustain peace. First, successful renegotiations maintain a patron's involvement by reducing the alliance costs when the patron is not strongly committed. Second, a large cost-sharing demand causes negotiations to fail, but it simultaneously signals the patron's continued commitment and panders to domestic isolationism. In the latter case, the patron's commitment and its cost-sharing demand are positively correlated. I demonstrate the empirical plausibility of these mechanisms through case studies of the US-Japan alliance in 1978 and 2019.
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Trapping a Friend: How do Arms Transfers Constrain Alliance Partners? (with Yasuki Kudo). Under Review. Presented at MPSA 2024.
Abstract
Why does the US transfer arms not only to close allies but also to states that may later challenge US interests? We analyze a formal model in which arms transfers and arms buildup are endogenous. A hegemon transfers arms to its partner, bearing in mind the partner's future arms buildup and the uncertainty of a future conflict. The model reveals a constraining effect. Arms transfers replace arms buildup by increasing its marginal costs. Reliance on arms transfers gives the hegemon greater influence over the recipient and restrains it from making demands that are not aligned with the hegemon's interests. Our empirical analyses confirm two implications derived from the model: the US transfers more arms to countries expected to grow militarily, and recipients of greater transfers are less likely to initiate conflict. This research offers a systematic explanation of how the US pursues its ideal world order through arms transfers.
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The Power of the President of the UN Security Council. Presented at ISA 2023 and APSA 2023.
Abstract
How do weak countries achieve their diplomatic goals in international organizations? I investigate this question in the context of the UN Security Council and its president. I argue that the elected UNSC members alter collective UNSC decisions through the UNSC presidency. By leveraging the alphabetical-order rotation of the president and applying the keyword-assisted topic model to the resolutions from 1992 to 2016, I analyze the effect of the president on the UNSC resolutions. The results affirm the strong influence of the president. Resolutions about (nuclear) weapons are likely to be adopted when the president's preference is close to the United States, whereas ceasefire-related resolutions are likely to be passed when the president's preference is different from the United States, possibly because these countries try to lock in the Council's involvement. Also, resolutions related to humanitarianism are likely to be adopted when the president has a democratic regime. This article reveals how weak countries are empowered by rules and how they shape the course of power politics.
Work in Progress
Others
Translation
- Diamond, L. (2019). Ill Winds: Saving Democracy from Russian Rage, Chinese Ambition, and American Complacency. Penguin Books. Translated into Japanese by Maiko Ichihara, Yuji Masumura, Takuto Tokairin, Atsushi Sugii, and Ryohei Suzuki. [Publisher]