Why was the atomic bomb dropped on Nagasaki Japan?

Answer 1

The plan had always been to use the atomic bombs against Germany as soon as they were ready, but Germany was defeated before the bombs were finished. Within four days after the surrender of Germany the Targeting Committee met at Los Alamos, to recommend cities in Japan as targets for the atomic bombs. The criteria used were that the city had to be large enough that the blast effect of the atomic detonation would be measurable, preferably the target city should be more than three miles in diameter. And so an accurate assessment of the blast effect could be obtained, the Targeting Committee preferred Japanese cities which had not yet been heavily bombed. The US Air Force was conducting a heavy conventional bombing campaign against Japan, and already large portions, several square miles, of many of Japan's sixty-seven largest cities were nothing but heaps of ash. The US had switched to using incendiary (fire) bombs against Japanese cities, which were largely paper and wood, and thus extremely flammable. The Targeting Committee recommended four cities as potential nuclear targets: Kyoto, Hiroshima, Yokohama, and the arsenal city of Kokura. Henry Stimson, the Secretary of War, had honeymooned in Kyoto, which was the ancient capital of Japan, and had it taken off the target list for sentimental reasons. The other three cities were taken off the conventional bombing list of acceptable targets, to preserve them as pristine nuclear targets. The first bomb, "Little Boy" was dropped on Hiroshima August 6, 1945. Three days later the second bomb, "Fat Man' was to be dropped on Kokura. Nagasaki was a secondary target for the mission, in case weather obscured visibility over Kokura. Nagasaki, a large seaport, had not been bombed except for one raid a little over a week before the nuclear attack. Weather scouting planes flying ahead of the nuclear bomber reported heavy cloud cover over Kokura, so the mission was switched to the alternate target, Nagasaki. Clouds thus saved Kokura and doomed Nagasaki.

due to the high civilian population

Answer 2

To force the Japanese to surrender and to see what would happen if a bomb of that sort was dropped on a city in a time when the US could still get away with it.