During the final stage of World War II, the United States detonated two nuclear weapons over the Japanese cities of Hiroshima and Nagasaki on August 6 and 9, 1945, respectively. The United States dropped the bombs after obtaining the consent of the United Kingdom, as required by the Quebec Agreement. The two bombings killed at least 129,000 people, most of whom were civilians. They remain the only use of nuclear weapons in the history of warfare.

In the final year of the war, the Allies prepared for what was anticipated to be a very costly invasion of the Japanese mainland. This undertaking was preceded by a conventional and firebombing campaign that destroyed 67 Japanese cities. The war in Europe had concluded when Germany signed its instrument of surrender on May 8, 1945. As the Allies turned their full attention to the war in the Pacific War, the Japanese faced the same fate. The Allies called for the unconditional surrender of the Imperial Japanese armed forces in the Potsdam Declaration on July 26, 1945—the alternative being "prompt and utter destruction". The Japanese ignored the ultimatum and the war continued.