@mumwon
they did carpet bombing of "normal" bombs of Tokyo just before Hiroshima - the death rate mostly caused by fires (wooden buildings) caused a direct death rate in the 10's of thousands.
100,000 plus in the firebomb raid of March 9/10 1945..in one night, plus maybe a 1,000,000 made homeless.
I suspect the reason they chose Hiroshima & Nagasaki, I suspect, is that they had NOT had that much bombing before &the US wanted to know how much damage a single bomb could caused to a city.
No reason to suspect it, it’s established historical fact that the US put certain Japanese cities (including but not exclusively Hiroshima and Nagasaki,) on a formal do not bomb list several months before A bomb strikes the exactly the reason you mention.
Probably the most authoritative source on this is Richard Rhodes,’s Pulitzer price winning book, “The Making of the Atomic Bomb”, but it’s probably not one many would fancy reading at the moment.