The Japanese were the ones bombed not the ones who bombed. And both A-bombs were necessary to bring the government to the peace table. Not to mention the little fact of 1,5 million Russians sweeping them from continental Asia.
Because they wanted the Japanese to give it up. Very simple answer. Anything else is hogwash. Read Richard Frank "Downfall"
The diplomatic records of the time would seem to argue against that opinion. There is a very good arguement supporting the fact that the bombs were an act of atomic diplomacy on the part of the US. They used them as an attempt to forestall Soviet ambition in the region. Read: Gar Alperovitz 'Atomic Diplomacy'
Japan is threatened with "a rain of destruction such as the world has never seen" if surrender is not forthcoming. Japanese military and diplomatic messages intercepted by the signals intell folks clearly indicated the Japanese had no intention of surrendering ... troop levels on Kyushu kept going up and up, directed by an army group HQ in Hiroshima so ... BOOM! goes Hiroshima ... casualties include some 30,000 Japanese soldiers. Japanese message circuits still indicate no plans to surrender and troops continue to move into Kyushu, now up to about 480,000. Obviously they aren't getting the message. Primary is socked in so divert to secondary ... BOOM! goes Nagasaki - major naval war production facilities and dockage. In Tokyo a captured American fighter pilot being interrogated tells his inquisitors that Tokyo was next. Suddenly they get the message ... Japan surrenders. Game, set match.
30.000 Japanese soldiers out of the approximately 60.000 killed at Hiroshima?! I find the number too high, but I might be wrong. And again, you are forgetting the little detail about the Red Army. Japan surrendered because it was facing three huge and very different threats: </font> Menace of massive American invasion —which can be successfully repelled, no matter the cost.</font> Menace of Soviet massive invasion, completely impossible to deal with it.</font> Menace to have more cities —Tokio included— banned from the face of the Earth by American 'special' bombs.</font> All those —and particulary the latter two— meant the complete destruction not only of Japan as a sovereign country but of the entire Japanese people.
Just happened to read the book: Hiroshima Diary: The Journal of a Japanese Physician, August 6-September 30, 1945: Fifty Years Later by Michihiko Hachiya, Warner Wells (Editor), John W. Dower Anyway, the author claimed that the army had almost all left the city because they knew the city would be hit hard sooner or later. I don´t know how many soldiers were really in the city at the time of the explosion but the author claims that not many.