The Iran–Iraq War was an armed conflict between the Islamic Republic of Iran and the Republic of Iraq lasting from September 1980 to August 1988, making it the 20th century's longest conventional war.It was initially referred to in English as the Gulf War prior to the Persian Gulf War of the early 1990s..The Iran–Iraq War began when Iraq invaded Iran via air and land on 22 September 1980. It followed a long history of border disputes, and was motivated by fears that the Iranian Revolution in 1979 would inspire insurgency among Iraq's long-suppressed Shia majority, as well as Iraq's desire to replace Iran as the dominant Persian Gulf state. Although Iraq hoped to take advantage of Iran's revolutionary chaos and attacked without formal warning, it made only limited progress into Iran and was quickly repelled; Iran regained virtually all lost territory by June 1982. For the next six years, Iran was on the offensive. A number of proxy forces participated in the war, most notably the Iranian Mujahedin-e-Khalq siding with Ba'athist Iraq and Iraqi Kurdish militias of Kurdistan Democratic Party and Patriotic Union of Kurdistan siding with Iran—all suffering a major blow by the end of the conflict..Despite calls for a ceasefire by the United Nations Security Council, hostilities continued until 20 August 1988. The war finally ended with Resolution 598, a U.N.-brokered ceasefire which was accepted by both sides. At the war's conclusion, it took several weeks for Iranian armed forces to evacuate Iraqi territory to honour pre-war international borders set by the 1975 Algiers Agreement. The last prisoners of war were exchanged in 2003..The war cost both sides in lives and economic damage: half a million Iraqi and Iranian soldiers, with an equivalent number of civilians, are believed to have died, with many more injured; however, the war brought neither reparations nor changes in borders. The conflict has been compared to World War in terms of the tactics used, including large-scale trench warfare with barbed wire stretched across trenches, manned machine-gun posts, bayonet charges, human wave attacks across a no-man's land, and extensive use of chemical weapons such as mustard gas by the Iraqi government against Iranian troops, civilians, and Iraqi Kurds. The United States, alongside regional and international powers, supported Iraq with loans, military equipment and satellite imagery during Iraqi attacks against Iranian targets. At the time of the conflict, the U.N. Security Council issued statements that "chemical weapons had been used in the war." U.N. statements never clarified that only Iraq was using chemical weapons, and according to retrospective authors "the international community remained silent as Iraq used weapons of mass destruction against Iranian as well as Iraqi Kurds." The UN Security Council did not identify Iraq as the aggressor of the war until 11 December 1991, some 12 years after Iraq invaded Iran and 16 months following Iraq's invasion of Kuwait.