From July 19 through August 2, 1945, the leaders of the United States, United Kingdom, and Soviet Union met at Potsdam to determine the postwar order and how to administer defeated Germany. During the Potsdam Conference deliberations, Soviet leader Joseph Stalin also agreed that the Soviet Union would enter the war against Imperial Japan 90 days after the German surrender on May 8. ... https://www.nationalww2museum.org/war/topics/end-world-war-ii-1945