Send message to Author

Paper short abstract

Japan is the only front-line US ally that both fears China and sees itself as a regional leader. The paper asks how the quiet fear of being left alone with China shapes Japan’s alliance behaviour, public narratives, and policy choices.

Paper long abstract

Debates on Japanese security policy usually focus on “normalisation”, the China threat, and the US-Japan alliance. This paper starts from a simpler point, one that is often taken for granted: Japan is the United States’ front-line ally against China, alone with no NATO-like community around it, but yet has a self-image as a “tier one” state that would not live under Chinese regional hegemony. The quiet fear of being abandoned by the US and left alone with China – a fear that cannot be stated openly in polite alliance and policy circles – nonetheless fundamentally shapes contemporary alliance politics.

The paper examines how this fear shapes Japan’s behaviour as a “reliable” ally and how it is managed in public language. Successive governments have worked hard to demonstrate Japan’s usefulness to Washington, through legal changes, military spending, build-up, and diplomatic activism, while avoiding open discussion of what US retrenchment would actually mean. Subordination to Washington is treated, implicitly, as the lesser of two evils: a way to insure against a future in which Japan must deal with China from a position of isolation and lowered status.

Drawing on speeches, white papers, Diet debates, among other sources, and focused on the post-Cold War era, the paper pays special attention to moments when US commitment seemed to waver – and how Japan responded. It shows how fear of abandonment is handled through reassurance towards the US, rather than through explicit debate about a future in which the US is less present

Send message to Author

Paper short abstract

This study traces the origins of U.S.-Japan defense cooperation by showing how the two countries began joint military planning in the early 1950s. Examining the actual practice of defense cooperation under domestic constraints, it reevaluates the U.S.-Japan security relationship during the Cold War.

Paper long abstract

In the wake of Russia’s invasion of Ukraine and growing concerns about a potential contingency involving Taiwan, the role of the U.S.–Japan alliance and specifically collective defense in a contingency—has taken on unprecedented importance. This study explores the historical origins of bilateral defense cooperation that are directly relevant to this contemporary concern.

It shows how the United States and Japan began to develop combined military plans in the early 1950s. The study clarifies points that existing works have not fully explained: why Japan, initially reluctant toward the formulation of these plans, later re-engaged in the planning process, and what negotiations took place behind the scenes. During these negotiations, the most divisive issue was the command relationship between the two forces—what kinds of command structures were considered between the United States and Japan? The study also demonstrates that, in the early 1950s, Japan sought approval of these plans by the highest governmental authorities in both countries. Furthermore, it illuminates the challenges faced by both the United States and Japan in balancing the military necessity of undertaking joint defense measures against the Soviet Union and other communist forces with the constraints of their respective domestic politics. These findings challenge the prevailing view that the plans were merely staff-level research by the two forces and instead reveal the early origins of collective defense in the U.S.–Japan alliance.

This study draws on extensive multi-archival research, particularly newly declassified materials from both U.S. and Japanese sources. By uncovering the actual practice of U.S.–Japan defense cooperation under domestic constraints, it offers a re-evaluation of the Cold War U.S.–Japan security relationship. Moreover, this study distinguishes itself from conventional scholarship by emphasizing not only the political and diplomatic dimensions of the U.S.–Japan security relationship but also its military and, crucially, operational dimension—an aspect that has been largely overlooked. This approach offers novel insights into the fundamental nature of the U.S.–Japan security relationship.

Send message to Author

Paper short abstract

This paper analyzes Japan’s reliance on US nuclear deterrence despite Article 9. It argues the constitution acts as a “committee of restraint,” paradoxically enabling deeper conventional integration and “counterstrike capabilities” while precluding indigenous nuclearization amidst regional crises.

Paper long abstract

Japan presents a unique paradox: it is the only democracy to constitutionally enshrine pacifism (Article 9) while relying explicitly on another state’s nuclear arsenal for security. This paper investigates how Tokyo reconciles its anti-nuclear national identity with an escalating dependence on U.S. extended deterrence amidst a volatile regional environment marked by North Korean missile tests, China’s nuclear modernization, and the normalization of nuclear coercion following Russia’s invasion of Ukraine.

Drawing on alliance theory, two-level game analysis, and literature on the nuclear taboo, the study traces Japan’s security evolution from the “Three Non-Nuclear Principles” through successive crises to the watershed 2022 National Security Strategy. The analysis argues that Japan is pursuing a strategy of “maximizing extended deterrence under strategic ambiguity.” By leveraging interpretive flexibility within Article 9, Tokyo deepens security cooperation—such as real-time intelligence sharing and “counterstrike capabilities”—while maintaining domestic constraints that preclude public discussion of NATO-style nuclear sharing.

The paper highlights three key tensions: (1) credibility concerns regarding U.S. decoupling; (2) the ideological cleavage between the Hiroshima-Nagasaki anti-nuclear memory and conservative realism; and (3) the gap between public opposition to nuclear acquisition and elite moves toward contingency planning. Comparative analysis reveals that Japan’s trajectory diverges from Germany’s acceptance of nuclear sharing and South Korea’s mainstreaming of indigenous nuclear debates.

Ultimately, the study concludes that Article 9 functions not as an obsolete relic but as a domestic “committee of restraint.” Paradoxically, this constitutional constraint enables deeper conventional integration with the United States by reassuring neighbors of Japan’s non-nuclear intentions. However, this delicate balance faces mounting strain should the credibility of U.S. deterrence erode or a Taiwan contingency force a choice between constitutional principles and survival.

Keywords: Japan security policy, Article 9, extended deterrence, nuclear taboo, U.S.-Japan alliance, strategic ambiguity.

Send message to Author

Paper short abstract

The paper will analyze Japan's recent diplomatic policies of their impact on Japan's economic and security situation with regard to China and the U.S.'s attitude to propose future hedging strategies that maximize Japan's benefit.

Paper long abstract

Japan, a major middle power country in the Asia-Pacific, is facing another diplomatic challenge in 2026. China, Japan’s largest trade partner and security threat, has increased its assertiveness in the geopolitical dispute with Taiwan. Meanwhile, the United States, the pillar of Japan’s national security, is retreating into a protectionism that does not prioritize international peacebuilding over domestic economic interests under Donald Trump’s administration. While Japan still relies on both superpowers, the country's current prime minister Takaichi Sanae’s U.S.-favoring diplomatic policies are raising concerns regarding the future of the hedging strategy. This paper, on the basis of Japan’s diplomatic situation in 2026, compares Japan’s benefits from China and the U.S., analyzes the shortcomings of Japan’s recent diplomacy, and then offers a solution for the future. It argues that, firstly, based on the current context, Japan should adopt a China-leaning strategy for at least the next three years because the economic gains outweigh the destabilizing security reliance on the U.S. Secondly, Japan’s recent diplomatic strategy, although long-term beneficial, is overly pressuring its economy and security issues in the short term. Finally, Japan’s hedging strategy should be leaning towards China in the next three years to reduce economic and security pressure and prepare for the decoupling from China. Then, Japan can hedge back to the U.S. after it withdraws from protectionism.