|Part of the Persian Gulf Conflicts|
Clockwise from the top: Iranian soldiers wear gas masks to counter Iraqi chemical weapons; Iranian soldiers rejoice after Khorramshahr's liberation; Donald Rumsfeld and Saddam Hussein meet in Baghdad to discuss U.S. military aid to Iraq; Iranian oil platform burns after an attack by U.S. Navy in Operation Nimble Archer
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, they made only limited progress into Iran and were quickly repelled; Iran regained virtually all lost territory by June 1982. For the next six years, Iran was on the offensive.
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, as well as 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 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 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. At the time of the conflict, the U.N. Security Council issued statements that "chemical weapons had been used in the war." However, due to various outside pressures, the statements never clarified that only Iraq was using chemical weapons, and retrospective authors have claimed, "The international community remained silent as Iraq used weapons of mass destruction against Iranian[s] as well as Iraqi Kurds.
The Iran–Iraq War was originally referred to as the Gulf War until the Persian Gulf War of 1990 and 1991, after which it was referred to as the First Persian Gulf War. The Iraq-Kuwait conflict, while originally known as the Second Persian Gulf War, eventually became known simply as the Gulf War. The Iraq War from 2003 to 2011 has since been called the Second Persian Gulf War.
In Iran, the war is known as the Imposed War and the Holy Defence . In Iraq, Saddam Hussein had initially dubbed the conflict the Whirlwind War. It was also referred to as , in reference to the Battle of al-Qādisiyyah.