1. In 1945 an atomic bomb was dropped on Hiroshima.
2. In 1945 an atomic bomb was dropped over Hiroshima.
When I first read an English texbook pubished in Japan, the preposition before Hiroshima was "on" as in #1. However, in a revised edition, the preposition is "over" as in #2.
Do you think "over" is better than "on" in the sentence above?
"over' could have a couple of meanings here - the airplane carrying the bomb was over the city when the bomb was dropped and the bomb detonated over (above) the city, not on the city.