The Japanese military, known as the Self-Defence Force (SDF), has developed new roles both outside and within the US-Japan alliance to contribute to regional/ international security. The question is how has the Japanese security policymaking elite been able to bring about this critical change to the security policy practice in light of the domestic social and legal constraints that have traditionally prevented the expansion of Japan’s security role, in military terms, in regional and international affairs. This research introduces external military crises as a critical cause of this change in Japanese security policy. It argues that the security policymaking elite constructed or inflated elements of threat from an external military crisis as directly affecting both the international environment and Japan’s national security. This study will focus on all military crises faced by Japan in the post-Cold War period.