"'The nuclear bombs, since they were known to be killing civilians going about civilian business, were contrary to both the Hauge and Geneva conventions."
I don't know what the standard was then, but that's damned sure not the standard today. The standard today is will possible civilian casualties outweigh the military benefits. It's often an eye of the beholder sort of thing. Given the estimates of dead and wounded of invading Japan and that they rightfully believed that dropping the bombs could end the war, certainly seems legal by today's standards.