On this day in 1980, Saddam Hussein's Iraq invaded Iran, launching one of the 20th century's most deadly wars, killing over 1 million people and injuring over 100,000 with chemical weapons. ⠀
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Saddam's reasons for the invasion included stopping the export of the 1979 Iranian Revolution movement to Shia-majority Iraq which threatened the Sunni-dominated Ba'athist leadership. The Iraqi government initially welcomed the Iranian Revolution, which overthrew Shah Reza Pahlavi, who was seen as an enemy, but when Ayatollah Khomeini called on Iraqis to overthrow the Ba'ath government, it caused anger in Baghdad. Despite Khomeini's call, Saddam gave a speech praising the Iranian Revolution and calling for Iraqi-Iranian friendship. Khomeini, however, rejected Saddam's overture and called for Islamic revolution. Iran's new Islamic administration was seen as an irrational, existential threat, especially since the Ba'ath party was a secular one that discriminated against and posed a threat to the fundamentalist Shia movement in Iraq.
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Saddam also wanted Iraq to replace Iran as the dominant state in the Persian Gulf. He wanted to position himself as the defender of Arab monarchies/ dictatorships against a revolutionary democratic Islamic ideology. Saddam expected the local Arabs of Khuzestan, the province he invaded, to rise against the Iranian government and support him - however, the majority of local Iranian Arabs fought alongside Iranian forces. Iraq hoped to take advantage of Iran's post-revolutionary chaos and expected a decisive victory in the face of a weakened Iran. Iraq was also supported by the US via technological aid, intelligence, the sale of chemical and biological warfare technology and military equipment, and satellite intelligence. ⠀
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The Iraqi military only made progress for three months, and by December 1980 the invasion had stalled, Then the Iranian military started to gain momentum against the Iraqis and regained all lost territory by June 1982, pushing the Iraqis back to the pre-war border lines. The next five years, until the end of the war, saw Iran go on the offensive, gaining significant areas within Iraq.