Iraq invaded Iran in September 1980 in a dispute over the Shatt al-Arab waterway and regional influence, beginning an eight-year war of trench warfare, missile strikes on cities, and chemical weapons use that killed an estimated 500,000–1,000,000 people combined. Iranian border cities such as Khorramshahr and Abadan were besieged, shelled, or occupied, forcing roughly 1–1.2 million Iranians from Khuzestan province into the interior. Iraq, for its part, expelled well over 200,000 Iraqis it deemed of Iranian origin, including many Shia Faili Kurds who were stripped of citizenship and forced across the border into Iran, often with little warning. The war ended in a 1988 ceasefire that largely restored the pre-war border under UN Security Council Resolution 598.
Iraq under Saddam Hussein invaded Iran in September 1980, beginning an eight-year war fought largely along the shared border; both governments displaced border populations, and Iraq expelled tens of thousands of Iraqis of alleged Iranian descent, including Faili Kurds.
World Bank and UN Population Division series give Iran about 38.7 million and Iraq about 13.2 million in 1980. Displacement was concentrated in the border provinces - Khuzestan, Kermanshah and Ilam on the Iranian side, Basra and the Kurdish north on the Iraqi - and included Iraq's expulsion of Iranian-origin Faili Kurds.
The Correlates of War project gives 500,000 Iraqi and 750,000 Iranian deaths, and Britannica reports estimates exceeding 1,000,000 including 50,000-100,000 Kurds; the PRIO/Uppsala Battle Deaths Dataset gives 'more than 600,000'. Charles Kurzman's demographic reanalysis of the 1996 Iranian and 1997 Iraqi censuses found no sex-ratio deficit in the military-age cohorts consistent with those figures and points instead to government-derived totals of roughly 250,000 Iraqi and 155,000-183,000 Iranian dead — the basis for the low end. Both governments had reasons to inflate or conceal, and Iran's martyr registries and Iraq's records were never independently audited, which is what drives the spread.
Human Rights Watch's Anfal documentation records mass executions and disappearances of tens of thousands of Kurdish civilians, the destruction of some 2,000 villages and the repeated use of chemical weapons during the war, findings substantially adopted by the Iraqi High Tribunal in its 2007 Anfal judgment.
Iran, Iraq