Albert Einstein contributed indirectly to the development of the atomic bomb, which eventually was used to end World War II. Although a pacifist at heart, as well as a refugee from Nazi Germany, Einstein believed it was necessary to inform President Roosevelt regarding German scientists potentially having the upper hand in developing the "super-bomb," later identified as a nuclear weapon. He urged the President to begin a similar top-secret project known as the Manhattan Project, eventually leading to the successful creation of atomic bombs, subsequently dropped on the Japanese cities of Hiroshima and Nagasaki, resulting in the surrender of Japan and the ultimate conclusion of World War II.