Japan was about to surrender
Japan was about to surrender, see here http://www.ihr.org/jhr/v16/v16n3p-4_Weber.html as a matter of fact they had just recently installed a new government and the main election bid was to end the war with the allies. Japan wasn't full of mindless soldier - folk as the media has stereotyped it to have been - on the contrary, there were peace activists and it should be noted
|that on January 20, 1945, two days prior to his departure for the Yalta meeting with Stalin and Churchill, President Roosevelt received a 40-page memorandum from General Douglas MacArthur outlining five separate surrender overtures from high-level Japanese officials."
There is a real reason that the US dropped the atomic bomb - to prove to the Soviets that they had it and were willing to use it. And it work - a week after the bombs were dropped the Soviets declared war on Japan and showed solidarity with the allies.