After the 1979 Iranian Islamic revolution, relations between Iran and Iraq deteriorated. Iraq invaded, starting a costly eight-year war.
In September 1980, Iraq responded to a series of border skirmishes with Iran by mounting a full-scale ground invasion of the oil-rich Iranian border province of Khuzestan.
By the end of the month, Iraq had abrogated its 1975 treaty with Iran and reclaimed the Iranian-controlled part of the Shatt al-Arab waterway. Both countries had started bombing campaigns.
The Iranian revolution had replaced the Western-backed Shah Reza Pahlavi with Ayatollah Ruhollah Khomeini's radical Shia Islamic regime.
The Ayatollah sought to export his ideology to other Middle Eastern countries, including Iraq, where the ruling Sunni elite had long struggled to contain a restive Shia majority.
A wave of support for Ayatollah Khomeini swept Iraq's Shia community – stirring up opposition which went as far as an assassination attempt on then Deputy Prime Minister Tariq Aziz in April 1980.
Views differ, however, as to whether it was the domestic Shia unrest, the desire to defend the Middle East from Ayatollah Khomeini's radical ideology, or simply power-hungry opportunism, that led Iraq to attempt to invade its neighbour.