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The United States dropped two atomic bombs named [[Little Boy]] and [[Fat Man]] on the Japanese cities of [[Hiroshima]] and [[Nagasaki]] respectively, bringing the war between the US and Japan to a swift and decisive end. The morality of the use of the bombs is debated because of a fear of atomic technology, and because of the huge loss of civilian life (140,000 at Hiroshima, 70,000 at Nagasaki). U. S. officials have said that the cities as a whole were proper military targets (the Japanese 2nd Army was headquartered there), and that because the bombings ended the war so quickly, fewer Japanese civilians were killed than if the bombs had not been used. Starting a week in advance, the US dropped over five million of warning leaflets on Japanese cities, after the Hiroshima bombing, urging the Japanese to evacuate,<ref>[http://www.pbs.org/wgbh/amex/truman/psources/ps_leaflets.html Leaflets Dropped On Cities In Japan]</ref><ref>https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/csi-studies/studies/vol46no3/article07.html</ref>  but they did not.  

The United States dropped two atomic bombs named [[Little Boy]] and [[Fat Man]] on the Japanese cities of [[Hiroshima]] and [[Nagasaki]] respectively, bringing the war between the US and Japan to a swift and decisive end. The morality of the use of the bombs is debated because of a fear of atomic technology, and because of the huge loss of civilian life (140,000 at Hiroshima, 70,000 at Nagasaki). U. S. officials have said that the cities as a whole were proper military targets (the Japanese 2nd Army was headquartered there), and that because the bombings ended the war so quickly, fewer Japanese civilians were killed than if the bombs had not been used. Starting a week in advance, the US dropped over five million of warning leaflets on Japanese cities, after the Hiroshima bombing, urging the Japanese to evacuate,<ref>[http://www.pbs.org/wgbh/amex/truman/psources/ps_leaflets.html Leaflets Dropped On Cities In Japan]</ref><ref>https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/csi-studies/studies/vol46no3/article07.html</ref>  but they did not.  

Since the US used both of these nuclear weapons in 1945 no other country has used the atomic bomb in war. The bombs and subsequent surrender also prevented the annexation of Japan's northern islands by the Soviet Union <ref>http://www.afsc.org/newengland/pesp/DecisionToUseABomb.htm</ref><ref>http://www.americanheritage.com/articles/web/20050902-atom-bomb-hiroshima-nagasaki-enola.shtml</ref>.  

Since the US used both of these nuclear weapons in 1945 no other country has used the atomic bomb in war. The bombs and subsequent surrender also prevented the annexation of Japan's northern islands by the Soviet Union <ref>http://www.afsc.org/newengland/pesp/DecisionToUseABomb.htm</ref><ref>http://www.americanheritage.com/articles/web/20050902-atom-bomb-hiroshima-nagasaki-enola.shtml</ref> and deterred the Soviet Union from expansion in Europe.  

The atomic bombs used at Hiroshima and Nagasaki were ''fission'' weapons, which detonate with a massive explosion due to the release of the binding energy within the nucleus of the atom.  Specifically, neutrons in a rapid chain reaction split the nuclei of a heavy chemical element, such as plutonium or uranium, to cause the massive release of energy.

The atomic bombs used at Hiroshima and Nagasaki were ''fission'' weapons, which detonate with a massive explosion due to the release of the binding energy within the nucleus of the atom.  Specifically, neutrons in a rapid chain reaction split the nuclei of a heavy chemical element, such as plutonium or uranium, to cause the massive release of energy.