Einstein was born in the German Empire, but moved to Switzerland in 1895, forsaking his German citizenship the following year. In 1901, he acquired Swiss citizenship, which he kept for the rest of his life. In 1905, he was awarded a PhD by the University of Zurich. In 1933, while Einstein was visiting the United States, Adolf Hitler came to power. Einstein did not return to Germany because he objected to the policies of the newly elected Nazi-led government. 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 German nuclear weapons program and recommending that the US begin similar research. Einstein supported the Allies, but he generally denounced the idea of nuclear weapons.