The short Manhattan Project was started by President Harry Truman. Even of the bad fail result of the Japanese Army, Emperor Hirohito didn't accept to sign into treaty surrender paper. After that, Hiroshima and Nagasaki were selected. On August 6, 1945,a first bomb, named Little Boy, was dropped on Hiroshima killing an estimated 60 to 70 thousand people. Three days later, the second bomb, named Fat Man, was dropped on Nagasaki killing approximately 40,000 people, so then on August 15 Japan surrendered United States and its allies unconditionally. This officially ended World War II and let the world into the Atomic Age.