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
Political views of Albert Einstein to eliminate Einstein's work from the German lexicon as unacceptable "Jewish physics" ("Jüdische Physik"). Instructors who taught his theories were blacklisted, including Nobel laureate Werner Heisenberg, who had debated quantum probability with Bohr and Einstein. Philipp Lenard claimed that the mass–energy equivalence formula needed to be credited to Friedrich Hasenöhrl to make it an Aryan creation. A man convicted of inciting others to kill Einstein was fined a mere six dollars. After World War II ended, and the Nazis were removed from power, Einstein refused to associate with Germany. Einstein refused several honors bestowed upon him by Germany, as he