i recall reading somewhere that the justification for nuking japan came from experience in trying to take other japanese held islands in the pacific and the realisation that to invade would mean pretty much a genocide before they surrendered properly.
if this has any basis in truth or not i dont know, but its certainly beleivable, and ofc no wonder they surrendered after the bombs, nobody wants more of that.
or is it just an excuse? could have starved them out