|Mushroom cloud over Hiroshima|
Of course, the left wrings their hands over the bombings, with some even characterizing the bombings as "a crime against humanity." Other suggest that the bombings were not necessary: that the U.S. could have selected a different target to "demonstrate" the bomb that would not have resulted in civilian casualties, ignoring (i) that the United States had dropped 720,000 leaflets two days prior to the bombings warning the civilians to evacuate; and (ii) Japanese leaders were nonplussed by civilian deaths. The massive casualties of fire-bombed cities had not deterred them. It is well known that the Japanese leaders were prepared to sacrifice Japans soldiers and civilians to prevent an invasion, even going so far as to train children in using bamboo spears. Japan's Army finally looked forward to being able to meet the U.S. forces in open battle.
Others have suggested that the Japanese were ready to surrender (on their own terms), and that the entry of the Soviet Union into the war against Japan is what really tilted the decision. However, Germany had not surrendered until it was physically invaded and overwhelmed on its home ground, and with the fanaticism that the Allies had seen from Japanese in other Pacific battlegrounds, there is no reason to believe that Japan would have acted any differently. It was estimated that an invasion of Japan would take 1 year to successful completion; assuming civilians would participate in resisting any invasion, an estimate for the Secretary of War estimated between 1.7 - 4 million American casualties, including 400,000 to 800,000 fatalities, and 5 - 10 million Japanese fatalities (PDF). This, of course, does not include the number of British and Commonwealth troops, civilians, and Japanese that would die in simultaneous invasions in South East Asia, or those that would die in the Soviet campaign that was just beginning in Manchuria.
Yet others have suggested that the United States should have delayed, either in deciding to drop either of the atomic bombs, or before dropping the second bomb on Nagasaki; or tried to find "more humane" methods to end the war (all guess work of course). Yet, every day of delay meant more casualties, and, as noted, the deaths and wounded from an invasion would have been astronomical. The atomic bombs were the most humane method to end the war.
For additional reading, there is the excellent essay by Paul Fussell entitled "Thank God for the Atomic Bomb" (PDF). Also, there is a video from Bill Whittle on the topic.