Albert Einstein Einstein did not return to Germany. He settled in the United States and became an American citizen in 1940. On the eve of World War II, he endorsed a letter to President Franklin D. Roosevelt alerting him to the potential development of "extremely powerful bombs of a new type" and recommending that the US begin similar research. This eventually led to the Manhattan Project. Einstein supported the Allies, but he generally denounced the idea of using nuclear fission as a weapon. He signed the Russell–Einstein Manifesto with British philosopher Bertrand Russell, which highlighted the danger of nuclear weapons. He was
Albert Einstein theoretical physics or mathematics. He strongly advocated the idea of a democratic global government that would check the power of nation-states in the framework of a world federation. The FBI created a secret dossier on Einstein in 1932, and by the time of his death his FBI file was 1,427 pages long. Einstein was deeply impressed by Mahatma Gandhi. He exchanged written letters with Gandhi, and called him "a role model for the generations to come" in a letter writing about him. Einstein spoke of his spiritual outlook in a wide array of original writings and interviews. Einstein stated that