Everything that Japan did in WWII was a large mistake. Admiral Yamamoto was correct when he stated that Japan could never beat The United States no matter how well the Nazis did. He did not foresee nor live long enough to know about the A bombs but he would not have been surprised. In fact the Nuclear option merely prevented Japan from being defeated by a more substantial action by the Soviet Union. Stalin ended the Non Aggression Pact w/ Japan-that had been signed at the same time he did the same w/Hitler- on Aug 1 1945 & started action against Japanese forces in Manchuria & Korea. It would have been hard for Truman to land troops on Kyushu & tell the Soviets that they could not land in Hokkaido. This would have led to a divided Japan maybe just North of Tokyo.