The Expansion of Europe–Japan Security Cooperation: Converging Threats and Diversifying Partnerships

Since the latter half of the 2010s, security cooperation between European countries and Japan has expanded and deepened markedly. This paper analyzes the drivers, substance, and implications of this development by examining Japan’s evolving security relationships with NATO, the European Union, and key European states, including the United Kingdom, France, Italy, and Germany. While existing literature has documented the gradual evolution of Anglo-Japanese, Franco-Japanese, and NATO–Japan cooperation, this study advances the literature by providing a more comprehensive and systematic account of how and why Europe–Japan security cooperation has intensified in recent years. The paper argues that this expansion has been driven by three interrelated factors. First, structural changes in the international security environment—most notably China’s rapid military rise and Russia’s attempts to revise the status quo by force—have strengthened strategic incentives for European countries and Japan to cooperate in defending a rules-based international order. Second, shifts in U.S. posture toward the liberal international order over the past decade have altered the strategic calculations of both European countries and Japan. As the United States has become less willing to underwrite the liberal order unconditionally and more explicit in prioritizing national interests, Europe and Japan have sought to diversify their security partnerships. Third, changes in Japan’s own security policy—especially the relaxation of restrictions on defense equipment exports and the enactment of the 2015 security legislation—have expanded the legal and institutional scope for security cooperation beyond the U.S.- centered alliance framework. Empirically, the paper traces the expansion of Europe–Japan security cooperation across three domains. The first is defense equipment development, highlighted by initiatives such as the Global Combat Air Programme (GCAP) involving Japan, the United Kingdom, and Italy, as well as Japan’s new efforts to promote cooperation with the European Union under the Security and Action for Europe (SAFE) framework. The second domain is the institutionalization of cooperation through mechanisms such as Acquisition and Cross-Servicing Agreements and Reciprocal Access Agreements, which have facilitated operational access and logistical support. The third domain is the growing frequency and sophistication of joint exercises involving maritime, air, and land forces. Particular attention is given to the deepening of operational ties between Japan and the United Kingdom, as well as between Japan and France. The paper concludes by assessing the strategic implications and remaining challenges of Europe–Japan security cooperation. Although recent developments indicate increasing coordination and interoperability, important challenges remain. While joint defense industrial projects such as GCAP demonstrate progress, questions remain regarding whether the European Union and individual European states can move beyond flagship projects to establish sustainable, long-term cooperative frameworks, including resilient supply chains. In addition, issues of power projection, sustainability, and reciprocity persist—particularly with respect to whether European states can maintain a meaningful presence in the Indo-Pacific and whether Japan is prepared to engage more actively in European security contingencies. How these challenges are addressed will shape the future trajectory of Europe–Japan security cooperation.