This book offers a comprehensive overview of Japan's national security institutions and policy today, including a detailed discussion of Japan's regional security environment and its alliance with the United States in the context of the Democratic Party of Japan's rise to power in August 2009. 2010 marks the 50th anniversary of the revision of the U.S.-Japan Security Treaty, making Japan one of the United States's longest and most important military allies. Over 40,000 US troops are based in Japan, as is the only U.S. aircraft carrier based outside the United States, the USS George Washington. Japan possesses one of the world's largest economies and strongest military forces, and as a result, its national security policies and institutions are highly significant—not just to America, but to the rest of the global community as well. This book provides an overview of Japan's transformation into one of the world's most capable military powers over the past 150 years. Particular attention is paid to developments in the past decade, such as the 2009 change in the controlling political party and Japan's responses to new global security threats.