Harry Truman became president of the United States on April 12, 1945 upon the death of Franklin D. Roosevelt. During Truman's presidency Germany surrendered (May 8, 1945) and Japan surrendered (Aug. 14, 1945), ending World War II.
The U.S., with Truman's approval, dropped an atomic bomb on the people of Hiroshima on Aug. 6 and one on Nagasaki on Aug. 9, 1945. As more information has become available regarding the Japanese peace effort, the Japanese fear of losing their emperor (whom they believed was a god), and U.S. advisors who offered other methods of winning the war, the debate has grown over whether the atomic bombings were necessary to save lives and win the war (for example, see Hiroshima: Was it Necessary?
Truman always staunchly defended the atomic bombings. Shortening the war, saving American lives, and revenge are the main reasons he gave for using them. In his first public explanation (Aug. 6, 1945, just after Hiroshima was a-bombed), he said:
"The Japanese began the war from the air at Pearl Harbor. They have been repaid many fold."
("Public Papers of the Presidents: Harry S Truman, 1945", pg. 197).
On Aug. 9, after Nagasaki was a-bombed, Truman made another public statement on why the atomic bombs were used:
"Having found the bomb we have used it. We have used it against those who attacked us without warning at Pearl Harbor, against those who have starved and beaten and executed American prisoners of war, against those who have abandoned all pretense of obeying international laws of warfare. We have used it in order to shorten the agony of war, in order to save the lives of thousands and thousands of young Americans."