Saddam hoped to exploit the turmoil after Iran's 1979 Islamic Revolution, seize the Shatt al-Arab waterway and the oil-rich province of Khuzestan, and prevent Ayatollah Khomeini's revolution from spreading to Iraq's Shia majority. Iraqi air strikes on Iranian airfields failed to destroy Iran's air force. Iran's resistance stiffened, and by 1982 it had retaken most of its lost territory. The war became a bloody stalemate that killed around half a million people before a UN-brokered ceasefire in August 1988.
Relations between the two countries had collapsed after the Iranian revolution. Khomeini called for the overthrow of Iraq's secular Ba'athist government, and there were border clashes through the summer of 1980. Saddam, who had become president in 1979, believed Iran's armed forces were in disarray after purges of officers and the loss of American support.
On September 22, Iraqi aircraft bombed ten Iranian airbases, attempting to copy Israel's surprise strikes of 1967, but most Iranian planes were in hardened shelters. The next day six Iraqi divisions crossed the border. They took the city of Khorramshahr after weeks of street fighting but failed to capture Abadan and its refinery.
The war drew in the wider world. Many Arab states and Western governments backed Iraq, fearing Iran's revolution; Iran used waves of young volunteers in offensives. Iraq used chemical weapons against Iranian troops and against Kurdish civilians in Halabja in 1988. Both sides attacked oil tankers in the Persian Gulf and fired missiles at each other's cities. Neither gained much: the ceasefire of 1988 left the border roughly where it had been.
Key people: Saddam Hussein, Ruhollah Khomeini