Dawn of a Thousand Suns: or how a letter made the Bomb unavoidable

The history of the development of nuclear weapons starts with the Einstein-Roosevelt correspondence. On 11 October 1939 the US President, Franklin D. Roosevelt, received a letter from Albert Einstein. The letter asked the US Administration three things: to coordinate with the community of American scientists working on the chain reaction; to secure research funds (also by rationalizing already existing efforts); and to address the problem of uranium ore, at the time scarcely available in the US. This event opened up a chain of events which ultimately led to the Manhattan project and to the use of atomic weapons on Hiroshima and Nagasaki. This article considers the likelihood of counterfactual developments, by taking into account intentions, degree of commitment, and reliability of plans on the sides of both the scientific community (led by Leo Szilárd) and of the US Administration (led by F.D. Roosevelt).