why did einstein write a letter to franklin roosevelt

Albert Einstein wrote a letter to President Franklin D. Roosevelt on August 2, 1939, to warn him about the potential development of "extremely powerful bombs of a new type" using uranium, derived from recent discoveries in nuclear physics. The letter, largely drafted by physicist Leo Szilard and signed by Einstein to leverage his influence, conveyed concern that Nazi Germany might be working on such bombs, and urged the U.S. to accelerate research and development in uranium-based weapons. This letter helped spur the U.S. government’s efforts that eventually led to the Manhattan Project and the creation of the atomic bomb. Einstein later referred to writing this letter as "the greatest mistake" of his life due to its grave consequences.