During the Cold War, the U.S.-Japan alliance was variously described as the cornerstone and the linchpin of U.S. Asia strategy, but over the past decade the role of this strategic alliance has come under increasing scrutiny. New dynamics in the Asia-Pacific region have prompted a rethinking of U.S. priorities in Asia. China's rise has called for a more complex assessment in both Tokyo and Washington of the circumstances under which the alliance might be tested. Japan's struggle with slow economic growth and a rather unpredictable effort at political reform has made strategic adjustment difficult. Similar concerns in the United States over its own economic recovery and stalled politics in Washington during the Obama administration's second term infuse the policy debate over the implementation of the "rebalance" to Asia.
Yet underlying these concerns is an important but less appreciated change in the U.S.-Japan alliance. For the past half century, Japan has played a supporting role in U.S. regional strategy, while maintaining limited military forces and relying on the United States to deter potential adversaries and, if necessary, assist in Japan's defenses. The U.S. extended deterrent was sufficient to keep Japan secure, and the forward deployment of U.S. forces in Japan provided a valuable platform for U.S. military presence in the Asia-Pacific. Much of the alliance-management agenda thus focused on Japan's provision of support for U.S. operations elsewhere. Over the past decade, however, the regional strategic balance has shifted, and the notion that Japan may find itself the target of attack has slowly permeated the security planning community in Tokyo.