answer:No man can say. The Japanese were probably as terrified of a Russian invasion from the west as they were from the American invasion or even nuclear weapons. By 1945 it seemed clear to many senior Japanese military that there was no way they could possibly win the war. Though you can argue that the nukes sealed the deal as far as a quick unconditional surrender goes. Propaganda played a huge role in Japanese intransigence. A lot of people genuinely believed that the Allied forces would enslave them, kill them all, or commit other atrocities. Dispelling such propaganda would have been difficult, probably not as expedient as simply dropping two nukes. By the way, more Japanese people were (probably)* killed in the incendiary bombing raids on Tokyo than in either Hiroshima and Nagasaki. *(caveat comes from later radiation deaths from nukes). To me, the horrifying use of nuclear weapons in World War II is not really separate from the careless or even deliberate targeting of Axis civilians in bombing raids that occurred throughout the war.