The Open Door Policy was equally opaque to Japan, leaving its restless army and highly competent naval leaders to think for the first time about a possible conflict with the United States. Mahan's commercial realpolitik may have died at Corregidor, but Hay's hope for a special relationship with China did not. Franklin Roosevelt and presidents since Richard Nixon have nurtured policies that assumed the United States could form some kind of partnership with an emphasis on trade and investment with a China that is both strong and, one hopes, democratic. The decades between the communist victory in 1949, punctuated by the Korean War, and the Nixon visit proved to be a temporary break in those basic American aspirations. What has evolved in the last century is the role of a U.S. security presence in Asia.
Japan is no longer the enemy and the Soviet Union has vanished.
But Japan remains at the core of U.S. security policy. The United States not only undergirds Japanese security, the American military presence also, sotto voce, prevents Japan from becoming Asia's premier military power once again with all the historic consequences that could involve. American security doctrine since the Korean War has also dictated that South Korea must not be destabilized by outside forces, and the presence of two U.S. divisions in place since 1954 guarantees stability and minimizes the risk of a second attack from the North. Little is likely to change this equation until and unless the two Koreas are peacefully unified. Peaceful unification of China has also been central to U.S. policy since 1950.