Atomic bombings of Hiroshima and Nagasaki

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The mushroom cloud over Hiroshima after the dropping of Little Boy

The Fat Man mushroom cloud resulting from the nuclear explosion over Nagasaki rises 18 km (11 mi, 60,000 ft) into the air from the hypocenter

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During the final stages of World War II in 1945, the United States conducted two atomic bombings against the cities of Hiroshima and Nagasaki in Japan.
After six months of intense strategic fire-bombing of 67 Japanese cities the Japanese government ignored an ultimatum given by the Potsdam Declaration. By executive order of President Harry S. Truman the U.S. dropped the nuclear weapon "Little Boy" on the city of Hiroshima on Monday, August 6, 1945,^[1][2] followed by the detonation of "Fat Man" over Nagasaki on August 9. These two events are the only active deployments of nuclear weapons in war.^[3] The target of Hiroshima was a city of considerable military importance, containing Japan's Second Army Headquarters, as well as being a communications center and storage depot.^[4]
Within the first two to four months of the bombings, the acute effects killed 90,000–166,000 people in Hiroshima and 60,000–80,000 in Nagasaki,^[5] with roughly half of the deaths in each city occurring on the first day. The Hiroshima prefectural health department estimates that, of the people who died on the day of the explosion, 60% died from flash or flame burns, 30% from falling debris and 10% from other causes. During the following months, large numbers died from the effect of burns, radiation sickness, and other injuries, compounded by illness. In a more plausible estimate of the total immediate and short term cause of death, 15–20% died from radiation sickness, 20–30% from flash burns, and 50–60% from other injuries, compounded by illness.^[6] In both cities, most of the dead were civilians.^[7][8][9]
Six days after the detonation over Nagasaki, on August 15, Japan announced its surrender to the Allied Powers, signing the Instrument of Surrender on September 2, officially ending the Pacific War and therefore World War II. Germany had signed its Instrument of Surrender on May 7, ending the war in Europe. The bombings led, in part, to post-war Japan adopting Three Non-Nuclear Principles, forbidding the nation from nuclear armament.^[10] The role of the bombings in Japan's surrender and the U.S.'s ethical justification for them, as well as their strategical importance, is still debated.^[11][12]