"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. Japan is one of the United States' most important economic partners. Outside of North America, it is the United States' largest export market and second-largest source of imports. Japanese firms are the United States' second-largest source of foreign direct investment, and Japanese investors are by far the largest foreign holders of U.S. treasuries, helping to finance the U.S. deficit and reduce upward pressure on U.S. interest rates. Bilateral trade friction has decreased in recent years, partly because U.S. concern about the trade deficit with Japan has been replaced by concern about a much larger deficit with China. The exception was U.S. criticism over Japan's decision in 2003 to ban imports of U.S. beef, which have since resumed."
CRS Report for Congress, RL33436