The most terrifying moment in history was Nagasaki, because they already knew what happened in Hiroshima.
Early nuclear weapons aren't modern fusion bombs. More Japanese were killed by conventional bombs and napalm.
And more than that, they simply didn't know how many we had... Which is actually a GOOD THING, because we spent the only two that were available, and the threat of us dropping lots more of them (which we didn't have) ended the war.