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.he discovery of nuclear fission by German chemists Otto Hahn and Fritz Strassmann in 1938, and its theoretical explanation by Lise Meitner and Otto Frisch, made the development of an atomic bomb a theoretical possibility.