Umm, that last claim is wholly untrue. Every nuclear-armed country (save perhaps a couple) has detonated nuclear bombs. The US isn't even the only one to use it intentionally against civilians, since the French were actively studying the deleterious effects of fallout on their colonial subjects in French Polynesia, which is what led to the Rainbow Warrior state-sponsored terrorist attack against New Zealand. I'm sure that there are other cases of the USSR or some other nuclear power testing their own devices against civilian populations if I had a mind to check.

Perhaps "the US is the only country to detonate a nuclear weapon against civilians of a country with which it was at war" or "the only country to detonate a nuclear weapon as an act of war"

And to this day there are people who believe and argue that this was fair. Propaganda is louder than a nuke.

Those certainly were appalling and destructive events. But why give them some special status over other bombing raids like the March 9 fire bombing of Tokyo, which also killed over 100,000 people in one night? Dropping 1 bomb vs. dropping 1,600 tons of conventional bombs in 3 hours?

Your title would read better if you changed the second “against” to “of”, OP.

...and used them against civilians.