Why did President Harry Truman decide to hit the Japanese cities of Hiroshima and Nagasaki with two atomic bombs in 1945?

President Harry S. Truman, warned by some of his advisers that any attempt to invade Japan would result in horrific American casualties, ordered that the new weapon be used to bring the war to a speedy end. On August 6, 1945, the American bomber Enola Gay dropped a five-ton bomb over the Japanese city of Hiroshima.