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
Religious and philosophical views of Albert Einstein the only opponent of Communism?" Einstein replied, "I don't have to emphasise that the Church ["sic"] at last became a strong opponent of National Socialism, as well." Einstein's secretary Helen Dukas added, "Dr. Einstein didn't mean only the Catholic church, but all churches." When the convert mentioned that family members had been gassed by the Nazis, Einstein replied that "he also felt guilty—adding that the whole Church, beginning with the Vatican, should feel guilt." (September 1948) When asked for more precise responses, Einstein replied: "About God, I cannot accept any concept based on the authority of the Church. [...] As