1. The Einstein–Szilárd letter was a letter written by Leó Szilárd and signed by Albert Einstein that was sent to the United States President Franklin D. ... It prompted action by Roosevelt, which eventually resulted in the Manhattan Project developing the first atomic bombs.
2. The Manhattan Project was the US government program during World War II that developed and built these first atomic bombs. Detonation of these first nuclear bombs signaled arrival of a frightening new Atomic Age.
