In the decades leading up to the Japanese invasion of China the religious deviation of Shintoism - or a different sect called Bushido (
http://en.wikipedia.org/wiki/Bushido ) took root in the Army which eventually took control of the government. While the Emperor was still worshiped as a living God, the Way of The Warrior was the principal path. Japan had never fully come out of its self imposed isolationist polices up through the 19th Century. While they imitated a great deal (and still do) of western culture and fashion many of the ancient traditions carried through still to this day. Under Bushido, as was with Nazism, the manifest destiny of a superior race was obvious to the Japanese upper class and military leadership. This lead to the enslavement of Korea and absolutely brutal invasion of China. When the US cut off oil and scrap metal imports to Japan, economically their backs were against the wall. They were forced into the military expansion into the Asian Sphere of Co-Prosperity before they were really ready.
So you take a culture that has not really assimilated western more's and values, is imbued with a cultural inferiority complex and a religious code of being a superior race... Then the cultural individual strictures of obedience, extreme formality, along with a group identity as opposed to any kind of individual one. You have a recipe for the Rape of Nanking and the destruction of life at the wholesale level though the Pacific. Because of a group identity as opposed to an individual one; the value of life in the East is much lower than in the West.
The decision to drop nuclear weapons were ones that haunted those who were part of the process the rest of their lives. In truth, from researching the question for over forty years now... It was the only rational decision that could be made. The Japanese war plans for the defense of the home islands were declassified, translated, and published some years ago. These plans included every man, woman, and child in Japan. It would start at the waters edge and end only in death for the invader or the defender. In depth, interconnected fields of fire of everything from spears on up was planned. Suicide weapons were planned for on the sea, in the air, and ground. Fighting would of been going on quite easily into 1950. Japan would of been a bombed out series of island with its infrastructure destroyed with only a token population left. Allied casualties would of been almost unbelievable. Tarawa, Okinawa, and Iwo Jima would of been the way to describe the battle for Japan. The US generation that fought in WWII took a serious hit in the casualties that had taken place already. The invasion of Japan would been our equivalent of what WWI did to the gene pool of France and England. The very nature of the American people would of been changed forever.
The bombing of Hiroshima and Nagasaki was the most inhumane, humane act in the history of the world. When I was much younger I spent a great deal of time in Hiroshima. Peace Park which was the island connecting to the bridge that was the aiming has been a mass grave for over 100,000 bodies or what could be found. Countless others were vaporized or consumed by the fire storm. What caused such a incredible level of destruction is the fact that Hiroshima sits in a alluvial plain/delta. The blast wave reflected off the surrounding hill sides 2-3 times. Along with the blast, the heat was also reflected into this churning mass of debris which much of which was wood. Most of Hiroshima at the time was wood frame post and beam construction with with masonry or concrete construction. The bomb created it's own fire storm. The remains of the bombing can still be seen today on the still standing bridge and A Bomb dome near ground zero. Hiroshima also has a remarkable research hospital for radiation illnesses. Birth defects one or two generations removed from the bombing were starting to be seen. Not unlike what is seen in Iraq in the area where Nerve Agent and Mustard Gas was used against the Kurds in the 1980's.
It could of been worse. Hiroshima was a secondary target. The primary was Kyoto, home to hundreds of ancient Japanese shrines. The destruction of those would of been tragic and actually been counter productive.
The damage and death rate at Nagasaki were not near like those in Hiroshima. Nagasaki, also a major port city, is not on a plain but on rolling hills which shielded many buildings and much of the population.
There was one man who was in Hiroshima and Nagasaki when both were bombed. I don't know if it was good luck he survived or not.
If we had not bombed Hiroshima and Nagasaki I don't believe we could of prospered as we did in the 50's and 60's. It was the only choice.
Just a few idle thoughts over lunch.