The Iran–Iraq War was an armed conflict between Iran and Iraq lasting from 22 September 1980, when Iraq invaded Iran, to August 1988. The war 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 Shi'ite 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.
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 trenches, manned machine gun posts, bayonet charges, "human wave attacks", and extensive use of chemical weapons by Iraq, and later deliberate attacks on civilian targets. The world powers United States and the Soviet Union, together with many Western and Arab countries, provided support for Iraq, while Iran was largely isolated. After eight years of war, war-weariness, lack of international sympathy as Iraq was targeting Iranian civilians with weapons of mass destruction, and increasing tension between Iran and United States eventually led to a UN-brokered ceasefire.