"The post-World War II U.S.-Japan alliance has long been an anchor of the U.S. security role in East Asia. The alliance, with its access to bases in Japan, where about 53,000 U.S. troops are stationed, facilitates the forward deployment of U.S. military forces in the Asia-Pacific, thereby undergirding U.S. national security strategy. For Japan, the alliance and the U.S. nuclear umbrella provide maneuvering room in dealing with its neighbors, particularly China and North Korea. The Bush Administration has made significant strides in its goals of broadening U.S.-Japan strategic cooperation and encouraging Japan to assume a more active international role. Following the September 11, 2001, terrorist attacks, Japan made its first-ever military deployments in non-combat support of U.S. and allied forces in Afghanistan. In 2004 Tokyo sent non-combat troops to Iraq, despite considerable domestic opposition. Japan generally has supported the 'hardline' U.S. position in the Six-Party Talks on North Korea's nuclear program. In 2005 the U.S. and Japan announced a sweeping new agreement to strengthen military cooperation. The plan calls for U.S. forces to be realigned and Japan to take on a more active (non-combat) role in maintaining regional and global security."
CRS Report for Congress, RL33436