Teller continued his research in Germany but when Adolf Hitler came to power in 1933 he decided to move to England. Two years later he emigrated to America and taught at George Washington University before moving to the University of Chicago.
In 1943 Teller joined Robert Oppenheimer, Enrico Fermi, David Bohm, James Franck, James Chadwick, Otto Frisch, Emilio Segre, Eugene Wigner, Felix Bloch, Leo Szilard and Klaus Fuchs on the Manhattan Project. Over the next few years Teller developed the atom bombs dropped on Hiroshima and Nagasaki. He also worked on developing the H-bomb (1946-53).
In 1953 Teller was appointed as professor at the University of California. The following year Teller was a key witness against his colleague, Robert Oppenheimer, who was considered a security risk because he objected to the development of the hydrogen bomb. Unlike Oppenheimer, Teller disagreed with the idea that a scientist should consider the moral implications of research.
The author of Our Nuclear Future (1958), Teller opposed the 1963 test-ban treaty. It was Teller who convinced President Ronald Reagan of the feasibility of the Star Wars Project for militarizing space with fission-bomb-powered X-ray lasers.
If we had made a demonstration and that had failed, then I think dropping the bomb would have been justified in order to end the war. To drop it without warning was wrong. It was wrong on moral grounds - it killed; it was wrong, although I could not see that at the time, on practical grounds because the dropping of the bomb has distorted our views, has changed our whole outlook. We are not now looking on the accomplishment of atomic explosions as progress which can, and should, be used in the right way. We had started at that time to look at it as something horrible, something that should not be continued.