The United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki in August 1945, during the final stage of the Second World War.The two bombings, which killed at least 129,000 people, remain the only use of nuclear weapons for warfare in history.n preparation for dropping an atomic bomb on Hiroshima, U.S. military leaders decided against a demonstration bomb, and against a special leaflet warning, in both cases because of the uncertainty of a successful detonation, and the wish to maximize psychological shock.