The Iraqi invasion of Iran began on 22 September 1980, sparking the Iran–Iraq War, and lasted until 5 December 1980. Ba'athist Iraq believed that Iran would not respond effectively due to internal socio-political turmoil caused by the country's Islamic Revolution one year earlier. However, Iraqi troops faced fierce Iranian resistance, which stalled their advance into western Iran. In two months, the invasion came to a halt after Iraq occupied more than 25,900 square kilometres (10,000 sq mi) of Iranian territory.
On 10 September 1980, Iraq, hoping to take advantage of a weakened Iran's consolidation of the Islamic Revolution, forcibly reclaimed territories in Zain al-Qaws and Saïf Saad; these had been promised to Iraq under the terms of the 1975 Algiers Agreement, but were never actually transferred. Both Iran and Iraq later declared the treaty as null and void, doing so on 14 September and 17 September, respectively. As a result, the only outstanding dispute along the Iran–Iraq border at the time of the Iraqi invasion on 22 September was the question of whether Iranian ships would fly Iraqi flags and pay navigation fees to Iraq while sailing through a stretch of the Shatt al-Arab spanning several kilometres. On 22 September, Iraqi aircraft pre-emptively bombarded ten Iranian airfields in an ultimately unsuccessful attempt to gain aerial superiority on the battlefield. On the next day, Iraqi troops crossed the international border in strength and advanced into Iran in three simultaneous thrusts along a front of approximately 644 kilometres (400 mi). Of Iraq's six divisions that were invading by land, four were sent to Iran's oil-rich Khuzestan in order to cut off Iranian access to the Shatt al-Arab and establish a territorial security zone.