The United States, at the order of President Harry S. Truman, dropped nuclear weapons on the Japanese cities of Hiroshima and Nagasaki on August 6 and 9, 1945, respectively, during the final stage of World War II. The United States had dropped the bombs with the consent of the United Kingdom as outlined in the Quebec Agreement. The two bombings, which killed at least 129,000 people, remain the only use of nuclear weapons for warfare in history.
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 was preceded by a U.S. conventional and firebombing campaign that destroyed 67 Japanese cities. The war in Europe had concluded when Nazi Germany signed its instrument of surrender on May 8, 1945, just after Hitler committed suicide. The Japanese, facing the same fate, refused to accept the Allies’ demands for unconditional surrender and the Pacific War continued. The Allies called for the unconditional surrender of the Japanese armed forces in the Potsdam Declaration on July 26, 1945—the alternative being “prompt and utter destruction”. The Japanese response to this ultimatum was to ignore it.
By August 1945, the Allies’ Manhattan Project had produced two types of atomic bombs, and the 509th Composite Group of the United States Army Air Forces (USAAF) was equipped with the specialized Silverplate version of the Boeing B-29 Superfortress that could deliver them from Tinian in the Mariana Islands. Orders for atomic bombs to be used on four Japanese cities were issued on July 25. On August 6, the U.S. dropped a uranium gun-type (Little Boy) bomb on Hiroshima, and American President Harry S. Truman called for Japan’s surrender, warning it to “expect a rain of ruin from the air, the like of which has never been seen on this earth.” Three days later, on August 9, a plutonium implosion-type (Fat Man) bomb was dropped on Nagasaki. Within the first two to four months of the bombings, the acute effects of the atomic bombings killed 90,000–146,000 people in Hiroshima and 39,000–80,000 in Nagasaki; roughly half of the deaths in each city occurred on the first day. During the following months, large numbers died from the effect of burns, radiation sickness, and other injuries, compounded by illness and malnutrition. In both cities, most of the dead were civilians, although Hiroshima had a sizable military garrison.
Japan announced its surrender to the Allies on August 15, six days after the bombing of Nagasaki and the Soviet Union‘s declaration of war. On September 2, the Japanese government signed the instrument of surrender, effectively ending World War II. The justification for the bombings of Hiroshima and Nagasaki is still debated to this day.