Before they decided to drop the bomb, FDR and his generals were planning "X Day", a massive campain into Japan. This would have involved thousands of soldiers and two fronts: the Russians were launching an attack on Jap troops in Mongolia, and the Americans were to take the large islands surrounding Japan before advancing to the main island. The calculations of death tolls on both sides were high. Too high. However, after the Russians had began their assult, the first atomic bomb was successfully detonated. The new president, Truman, decided that to issue and ultimatum demanding unconditional surrender. The Japs refused. So we dropped the bombs on Hirshima and Nagiskai (I'm sure I spelled those wrong). Now, there are many good reasons not to have dropped the bombs. First, and most obviously, the enormous loss of lives. That's never a good thing. Also, no one was aware of what might happen with all that radiation that was thrown up into the air. It came down, and (though I have no reporrts or anything to cite) considering the fact that it has to come down eventually, and whatever it came down on (oceans, people, other cities) would have become contaminated, and possibly have died. Also, leftover radiation would have left the areas where the bombs detonated severly poisonous. Another thing to know is that we were unsure that the bomb would actually work. The thing was mostly held together with duct tape, after all. If it hadn't worked detonated, it may have fallen to earth, relatively undamaged. The Japanesse could have possibly analyzed it, and built their own atomic weapons. That's all I can think of for now. Did that help any?

Sorry... can't help you there as I think they got it right by dropping the bomb. As Japan had stated that they would fight to the last man, an invasion by Allied (mostly US) troops would have been long and costly in lives (ultimately more than the two bombs). The only other option would have been a long and drawn out military blockade, which after Pearl Harbor wasn't a real option as far as the Americans were concerned. Drop the bombs... Japan surrenders... Boys are home for Christmas... good job all around. Hope this helps.