The Iran–Iraq War, referred to as the Imposed War and Holy Defense or Sacred Defense in Iran, began on 22 September 1980 when Iraq invaded Iran. It ended on 20 August 1988, when Iran accepted the UN-brokered ceasefire. Iraq wanted to replace Iran as the dominant Persian Gulf state and was worried the 1979 Iranian Revolution would lead Iraq's Shia majority to rebel against the Ba'athist government. The war also followed a long history of border disputes, and Iraq planned to annex the oil-rich Khuzestan Province and the east bank of the Shatt al-Arab (Arvand Rud).
Although Iraq hoped to take advantage of Iran's post-revolutionary chaos, it made limited progress and was quickly repelled; Iran regained virtually all lost territory by June 1982. For the next five years, Iran was on the offensive until Iraq took back the initiative in 1988, and whose major offensives led to the final conclusion of the war. There were several proxy forces—most notably the People's Mujahedin of Iran siding with Iraq and the Iraqi Kurdish militias of the KDP and PUK siding with Iran. The United States, Britain, the Soviet Union, France, and most Arab countries provided political and logistic support for Iraq, while Iran was largely isolated.
After eight years of war, war-exhaustion, economic devastation, decreased morale, military stalemate, lack of international sympathy against the use of weapons of mass destruction against civilians by Iraqi forces, and increased U.S.–Iran military tension all led to a ceasefire brokered by the United Nations.
The conflict has been compared to World War I in terms of the tactics used, including large-scale trench warfare with barbed wire stretched across fortified defensive lines, manned machine-gun posts, bayonet charges, Iranian human wave attacks, extensive use of chemical weapons by Iraq, and, later, deliberate attacks on civilian targets. A special feature of the war can be seen in the Iranian cult of the martyr, which had been developed in the years before the revolution. The discourses on martyrdom formulated in the Iranian Shia context led to the tactics of "human wave attacks" and thus had a lasting impact on the dynamics of the war.
An estimated 500,000 Iraqi and Iranian soldiers died, in addition to a smaller number of civilians. The end of the war resulted in neither reparations nor border changes.
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