It was the use of the Atomic Bomb. Having won the war in Europe, the Americans and their allies concentrated their efforts on the Far East. Japan refused to surrender despite the on-going bombings and destruction of her army. They also threatened to kill American POWs if they U.S. invaded Japan. Truman ordered the use of the atomic bomb. It was used in Hiroshima on August 6 then again on Nagasaki on August 9 resulting to Japan’s surrender.