Think about humans in Horoshima & Nagasaki. Probably more civilians killed in a short time by other humans in world history.
The death toll was higher in the fire bombing of Tokyo.
Firebombing of other major cities in Japan killed far more in a single bombing sortie. The B-29s dropped only incendiaries and the Japanese wooden homes with rice paper windows went up in huge flash fires. Documented on mission films released after the war. Deaths were civilians, and as most civilians who weren’t involved in agriculture/food production were involved in military plants (aviation, steel, small arms, ammunition- which was Nagasaki’s principal industry from the targeting data of Fat Man’s mission)— every civilian was “on the ground” for the final defense of the island.
Several excellent scholarly books have been written on this topic, as well as the “needless” bombings in the European theater. The issue of civilians killed in wars left the harbor back in the 1800’s worldwide.