Truman was vice president for only 82 days before President Roosevelt died.
He had very little significant discussions on world affairs and domestic politics after taking the oath of office for Roosevelt's vice president and was completely unaware of major initiatives to continue the successful war - most notably the secret project Manhattan, which at the time of Roosevelt's death, was on the highlight of testing the first atomic bomb.
Truman was soon briefed on the Manhattan Project and approved the use of nuclear weapons against Japan in August 1945 after the Potsdam Declaration was rejected by the Japanese Empire.
The atomic bombing of Hiroshima and Nagasaki remained to this day the first, but also the only, use of nuclear weapons for war purposes. The bombing was followed by the rapid capitulation of Japan on September 2, 1945, and the end of World War II. The use of nuclear weapons was not controversial at the time, both in the US and among its allies.
At the Potsdam Conference, Joseph Stalin advised Truman to use the atomic bomb as soon as possible. In the years following the bombing, Truman's decision became extremely controversial, and it was said why he decided to do so.
