The United States, the British Empire, and China had called for the unconditional surrender of the Japanese armed forces in the Potsdam Declaration (July 1945) but Japan didn't.
After the Hiroshima nuclear attack, the USSR declared war against Japan and attacked Manchuria, rapidly overwhelming Japanese positions there. Finally, a second U.S. atomic bomb was dropped on the Japanese coastal city of Nagasaki, which led to the surrender of Imperial Japan, bringing the hostilities of World War II to an end.
