1) In 1905, Einstein discovered that a large amount of energy could be released from a small amount of matter, though he did not consider weapons at the time due to his pacifism. 2) In the 1930s, Einstein changed his anti-war position due to the rise of Hitler in Germany, and in 1938 he consulted with physicists concerned about Germany's nuclear research. 3) In 1939, at Einstein's suggestion, a letter was written to Roosevelt warning about Germany's nuclear efforts and recommending the U.S. pursue similar research. This prompted Roosevelt to form the Briggs Committee to study nuclear fission.

1. Einstein and the Atomic Bomb