Why were atomic bombs used?

Answer 1

President Harry S. Truman reasoned that a full scale invasion of Japan would cost too many American lives and would still devastate the nation. The United States needed something spectacular too make the traditionally "death over defeat" nation surrender, and a conventional invasion would simply increase the Japanese war effort.

Answer 2

In World War II, the huge number of casualties on both sides in taking the tiny island of Iwo Jima was an indicator that the invasion of Japan, which was to start the week after the bombs were dropped, would be a bloodbath.

In Japan, there would be no issues with getting supplies to the Japanese troops, while the Allies would have exactly that problem. The fanatic part of the Japanese military and government pledged that they would fight to the death. This was because the Allies demanded unconditional surrender. Nobody told the Japanese leaders that they could keep their emperor, so nearly all Japanese would fight to keep him.

Although Japan's source of oil and metals had been disrupted by the Allies, Japan still had numerous stockpiles that they could have used had they been invaded.

With no chance of an unconditional surrender, President Truman followed his advisors' recommendations to order the dropping the A-bomb (Atomic bomb). At that point, the fanatics in Japan stated that they still would fight to the death; however, there was a second group of Japanese officials who wanted the war to stop immediately. At about the time that these people were starting to be heard, the H-bomb was dropped on Nagasaki. Most historians agree that this second bomb did not need to be used, but was anyway just to 'see if it worked'. On the other hand it was also used to decrease morale (spirit and hope)

In any event, after the Japanese surrendered, and after the Americans occupied the country and started rebuilding it, many Japanese army commanders stated during questioning that dropping the A-bomb was the right thing for the Allies to do. The lives lost from the A-bomb drop were around 80,000. The losses from an invasion of Japan were estimated at up to a million. Dropping the bomb seems to have been the more humane choice.