http://www.thenewamerican.com/culture/history/item/23288-dropping-the-bomb-why-did-the-u-s-unleash-its-terrible-weapon
No good evidence exists to demonstrate that the atomic bomb was needed to hasten the end of the war with Japan. While many Americans have been persuaded that a full-scale invasion of Japan and its accompanying huge number of casualties were avoided, no invasion was ever needed. Japan was beaten and was trying to surrender.