From a strategic and military aspect Japan would play an important role in case of a renewal of serious military action on the Korean peninsula. Not only because of its geographic location but also because of Japan’s military capabilities and the strong U.S. military presence in Japan. What is maybe less known is the importance of the United Nations Command (UNC) and its Rear Headquarters (HQ), located at Yokota Airbase in Japan. It was at Yokota Air Base Gen MacArthur set up the very first UNC HQ in 1950. After the Korean War, several of the UN Sending States (states providing military forces to the Korean War) and Japan signed a Status of Forces Agreement (SOFA), and the UNC main Headquarters moved to Seoul while maintaining the UNC Rear HQ in Yokota. Through this SOFA the U.S. and Japan mutually designated 7 bases for use by those UN Sending States who are signatories to the SOFA. Additional nations can join upon approval of the Japanese Government.
Find more info on this event hosted by the Institute of Security and Development Policy here.