This book argues that the transformation of Japan’s defense since 2012 has been triggered by the emergence of the first threat to Japan’s territorial integrity since 1945, namely China’s continual challenging of Japan’s control of the Senkaku Islands. It shows how this threat led to Japan building its own version of an A2/AD strategy and contributed to the demise of the prohibition on not procuring long-range missiles. It argues that the new security documents of 2022 that mandate increasing defense spending to 2% of GDP, is the culmination of this Senkaku-driven post-2012 defense transformation. Nonetheless, Japan’s defense transformation faces significant challenges, including geographic and demographic, base-community relations, and limited SDF capacity. This book analyzes the implications of Japan’s defense transformation for its involvement in a military conflict over Taiwan between China and the USA. It argues that the attitudinal defensive realism of the Japanese public and many elites explain why the confrontation over the small and remote Senkaku islands led to a transformation of Japanese defense, and why this transformation has been limited to territorial defense and is not leading Japan to play a military role beyond its borders.