Paper short abstract

This paper explores the transformation of Japan’s security alignment strategies with key Indo-Pacific and global actors in the post-Abe era. It argues that Japan is recalibrating its approach to emphasise issue-specific and pragmatic strategic partnerships, focused on selective coalition-building.

Paper long abstract

During the administration of former Prime Minister Shinzō Abe (2012–2020), Japan pursued a dual strategy of enhancing autonomous defence capabilities while simultaneously strengthening the Japan-US alliance. A third strategic pillar involved the expansion of security-oriented cooperative frameworks with a diverse array of partners at bilateral and minilateral levels, under the Free and Open Indo-Pacific Vision. Security alignment has remained a key aspect of Japanese strategic thinking in the post-Abe era. The growing tensions with China, Russia’s continuing war in Ukraine and uncertainties of the US defence commitments to Japan under the second Donald J. Trump administration, along with the steady rise of new security threats, have elevated further the strategic significance to Tokyo of non-US partners.

The proposed paper explores the transformation of Japan’s security alignment strategies with key Indo-Pacific and global actors from 2020 to 2025, addressing both traditional and non-traditional security challenges. The paper contends that, as the international system gradually transitions toward a “multiplex” order characterised by the absence of a singular hegemon (Acharya 2018), Japan is recalibrating its approach to emphasise issue-specific and pragmatic strategic partnerships. In an environment marked by a plurality of actors, intricate interdependencies and fragmented governance, Japan has refined its engagement with four principal partners: Australia, which remains vital for conventional defence and deterrence, particularly as a safeguard against potential US disengagement; the Philippines, which is central to countering China’s influence in the South China Sea and Southeast Asia; India, which is instrumental in upholding the rules-based maritime order and serves as a counterbalance to China, with its ties to Russia further incentivising deeper cooperation; and the European Union, which embodies Japan’s global commitment to the Liberal International Order and the mitigation of hybrid threats, thereby linking the Indo-Pacific and Europe. Through a comparative analysis of Japan’s relations with these actors, the paper elucidates the emergence of focused defence and security cooperation that advances coalition-building. The findings underscore the significance of pragmatic, interest-driven alignments in the context of an ever more uncertain and rapidly changing global security environment.

Paper short abstract

This paper examines Japan’s recent framing of a Taiwan contingency as a national security issue, arguing that it reflects a substantive shift in Japan’s Taiwan Strait posture. It highlights Japan’s growing role in shaping regional stability through alliance coordination and security signaling.

Paper long abstract

This paper argues that recent Japanese statements linking a “Taiwan contingency” to Japan’s national survival reflect a substantive transformation in Japan’s Taiwan Strait strategy rather than rhetorical escalation. Beijing’s unusually sharp response signals strategic alarm, as Japan’s evolving posture directly challenges core assumptions underlying China’s war planning.

Focusing on Japan’s shift from strategic ambiguity toward a more explicit Taiwan-centered security framework, the paper demonstrates that the outcome of a Taiwan Strait contingency depends less on cross-strait military asymmetry than on Japan’s strategic choices regarding alliance coordination, basing access, and logistical support. Drawing on recent war-gaming analyses and strategic assessments, it shows that China’s viable victory scenarios consistently emerge only when external intervention is neutralized through Japanese non-cooperation. Japan has thus become the decisive variable determining whether deterrence holds or collapses.

The paper situates this shift within Japan’s broader security policy evolution, including debates over alliance responsibilities and the geographic scope of national defense. While the primary focus is Japan’s strategic recalibration, the analysis also highlights how parallel changes in Japan–Taiwan relations reinforce this transformation. Expanded parliamentary exchanges, policy coordination, and security-relevant signaling have moved the relationship beyond economic and societal ties, providing political infrastructure for Japan’s emerging Taiwan Strait posture.

The paper concludes that Beijing’s heightened sensitivity reflects recognition that Japan’s Taiwan strategy has crossed a critical threshold. The Taiwan Strait must therefore be understood not as a bilateral flashpoint, but as a regional strategic system in which Japan functions as the war-deciding variable.

Paper short abstract

This paper analyzes Japan’s reinterpretation of collective self-defense through the concept of senshu-boei, with particular focus on “minimum necessary capability.” It examines the 2014 policy shift, implications for Taiwan, and Japan’s expanding denial-oriented security posture in the region.

Paper long abstract

Amid China’s rapid military expansion and increasingly assertive behavior in the South and East China Seas and the Taiwan Strait, Japan’s cabinet under the late Prime Minister Shinzo Abe approved the limited exercise of the right to collective self-defense in 2014, followed by security-related legislation in 2015. Existing scholarship largely attributes this shift to the cabinet’s reinterpretation of Article 9 of the Constitution, which renounces the use of force in international disputes. While this literature traces the post–Cold War evolution of Japanese security policy, particularly under Abe, it fails to explain the political, legal, and doctrinal conditions that enabled such reinterpretation.

This study addresses that gap by examining Japan’s evolving interpretation of collective self-defense through the framework of senshu-boei (専守防衛, exclusive self-defense), focusing on its core principle: hituyō saishōgen no nōryoku (必要最小限の能力, minimum necessary capability). How this standard is defined and reinterpreted is central to understanding Japan’s postwar military trajectory and future transformation. The paper also analyzes the implications of the 2014 reinterpretation for Taiwan’s security, where collective self-defense scenarios are most plausibly relevant, and examines Japan’s growing reliance on denial-oriented, cross-domain capabilities.

This analysis is timely as cross-strait tensions have intensified. China’s sharp response to Japanese Prime Minister Sanae Takaichi’s 2025 statement that a Taiwan contingency would threaten Japan’s survival, thereby indicating that it could be regarded as meeting the criteria for exercising collective self-defense, underscores the issue’s sensitivity. Because Taiwan’s security is closely linked to Japan’s own, interpretations of the “minimum necessary capability” carry significant strategic consequences. The paper concludes that if further reinterpretation becomes untenable, Japan may be compelled to move beyond senshu-boei and adopt the Ashida interpretation of Article 9, which permits the full use of collective and individual self-defense.