The book explains why Germany opposed the US decision to attack Iraq in 2003, whereas Japan supported it, despite the two countries' many similarities. Employing the concept of alliance security dilemma--constituted by the twin fears of abandonment and entrapment--the author argues that the two countries pursued opposite policies toward the Iraq War because the level of Germany's alliance security dilemma in its relationships with the US was higher than Japan's. The two countries' alliance security dilemma with the US, however, is not derived from the mere presence or absence of external threats. Instead, it is a product of (1) the regional security environments plus U.S. security commitment to the two countries, (2) the type of alliance institutions to which each country belongs, and (3) the characteristics of their military institutions. The author's conclusions are based on analysis of primary and secondary materials as well as interviews conducted with key political actors in both countries.