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Why did Albert Einstein write to President Franklin D. Roosevelt in 1939?

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U.S. hydrogen bomb test in the Marshall Islands — nuclear weapon A test of a U.S. thermonuclear weapon (hydrogen bomb) at Enewetak atoll in the Marshall Islands, November 1, 1952.

In 1939, Albert Einstein wrote to President Franklin D. Roosevelt at the urging of physicists Leo Szilard and Eugene Wigner.12

The letter was prompted by growing concerns within the scientific community that Nazi Germany might successfully develop a nuclear weapon following recent breakthroughs in nuclear fission. Einstein’s correspondence warned the president of this potential danger and advised the United States to establish its own nuclear research program.132

This initiative was a pivotal moment in the history of military technology, as it directly led to the formation of the Advisory Committee on Uranium and eventually the Manhattan Project, the secret U.S. effort that developed the first atomic bomb. It is a fundamental ethical principle that the pursuit of scientific knowledge should be guided by a commitment to human safety and the prevention of catastrophic destruction, a concern that Einstein and many of his colleagues later championed through their advocacy for international control of nuclear technology.14325