The Japanese refused to surrender, and if America had to stage an invasion and occupation of Japan, it could have been far more costly in lives and resources long-term. It could have been our Vietnam before Vietnam. Even one short raid of firebombing Tokyo caused comparable losses(according to official figures) to the Hiroshima bombing and a bit more than the bombing in Nagasaki, and being faced with an attack like this - being suffocated and broiled alive - is arguably more traumatizing and cruel compared to instant vaporization in the killzone of a nuclear blast.
"Masses of panicked and terrified Japanese civilians scrambled to escape the inferno, most unsuccessfully. The human carnage was so great that the blood-red mists and stench of burning flesh that wafted up sickened the bomber pilots, forcing them to grab oxygen masks to keep from vomiting.
The raid lasted slightly longer than three hours. “In the black Sumida River, countless bodies were floating, clothed bodies, naked bodies, all black as charcoal. It was unreal,” recorded one doctor at the scene."
- History.com
The official figures by the US and the Japanese of the casualties of the firebombing were placed at around one hundred thousand, but one could argue that both sides had reasons to doctor the numbers.
"With an average of 103,000 inhabitants per square mile and peak levels as high as 135,000 per square mile, the highest density of any industrial city in the world, and with firefighting measures ludicrously inadequate to the task, 15.8 square miles of Tokyo were destroyed on a night when fierce winds whipped the flames and walls of fire blocked tens of thousands fleeing for their lives. An estimated 1.5 million people lived in the burned out areas. Given a near total inability to fight fires of the magnitude produced by the bombs, it is possible to imagine that casualties may have been several times higher than the figures presented on both sides of the conflict."
"Overall, by one calculation, the US firebombing campaign destroyed 180 square miles of 67 cities, killed more than 300,000 people and injured an additional 400,000, figures that exclude the atomic bombing of Hiroshima and Nagasaki."
- https://apjjf.org/-Mark-Selden/2414/article.html
Regardless of the ferocity of conventional war, the Japanese were totally fanatical and refused to give up. This can be seen in the case of one Japanese officer Onada, who continued fighting the war from the jungles of the Philippines for nearly 30 years after it ended, in spite of all attempts to show him the truth. Once the equally barbaric and fanatical communist Russians started kicking their doors in from China, the old Bushido code of never surrendering and fighting until your death started to lose its attractiveness, especially once your nation was left with the choice between surrendering unconditionally to a civilized people and facing total annihilation with the world's superpowers picking over the scraps of what used to be your civilization. After all, there could be no vengeance and no honor after death if nobody was left alive to honor you.
Another thing to consider is, what if we didn't nuke Japan? Then the awesome, terrible powers of nuclear weapons and their effects on land & life may not be so intimately known until much later. Nuclear weapons were of very low yield at this time, and if the nuclear hysteria that it brought about for the cold war in our timeline never manifested, could this have led to a nuclear bombing later on? In actual history, we have come close on several occasions to nuclear war as it is. What if a bomb on orders of magnitude greater power like the Castle Bravo or the Tzar were dropped on a municipal center - or centres, as in the case of a nuclear war? Though I don't like delving into alternate history, if we look at the issue this way, the cost of early deployment of the bomb on an unfortunate Japan could have saved not only the lives of their contemporaries but also many unborn lives and the Earth herself in the future.
Now, this is not meant in defense of causing civilian casualties, nor is it to detract from the struggle of the survivors, though it should be known that civilian casualties are a natural and unavoidable occurence in war. The point here is that, though dropping nukes may not have been a good choice, given the circumstances, it may have been our best choice.
