It wasn’t even the most deadly bombing of the war. The target cities had to be specifically set aside from the conventional bombing raids so that there would be something left to destroy. It came at the end of a decade of intense fighting that saw tens of millions of civilians killed. It’s a remarkable event because it was a single plane with a single bomb rather than hundreds of planes and thousands of bombs, and that had a massive effect on world events afterwards, but the scale of human suffering of this bombing was, sadly, wholly unremarkable by that point.