well, to get back on topic. I'm not sure if it's been mentioned yet, but leaflets were dropped in all potential japanese cities the bombs could have been dropped, and well in advance. They didn't give a lot of details, but basically said "if you live in these cities, we're going to bomb them and you will die if you don't leave. So please, please leave. There may be other cities bombed, but these most definitely will, since there are major war-related installations placed in residential dense areas. You have been warned"
But they were mostly ignored, because the japanese government was pushing the narrative, to their citizens, the nation could not lose the war. An invasion would have been incredibly bloody, so of the options available it was...the lesser evil? arguably, who knows what other options were ignored at the time.
But as Jimmy Carter said: "War may sometimes be a necessary evil. But no matter how necessary, it is always an evil, never a good. We will not learn how to live together in peace by killing each other's children."