The Iran–Iraq War, which began with Iraq's invasion of Iran in September 1980, was a devastating eight-year conflict that ended with a UN-brokered ceasefire in August 1988, resulting in roughly 500,000 deaths and making it the deadliest conventional war between developing countries. Iraqi President Saddam Hussein launched the war to prevent Iran's new revolutionary ideology, led by Ruhollah Khomeini, from spreading to Iraq's Shia majority and to reclaim the eastern bank of the Shatt al-Arab river, which had been ceded to Iran in the 1975 Algiers Agreement. The war featured brutal trench warfare and Iraqi chemical attacks on civilians, with Iraq's initial advance stalling by December 1980, followed by Iran's recapture of its territory by June 1982 and a subsequent five-year Iranian offensive into Iraq. Iraq received support from the US, USSR, France, and most Arab countries, while Iran was aided by Syria, Libya, North Korea, and others, but the conflict ultimately ended in a stalemate with no permanent border changes or war reparations. Both nations suffered severe financial and military losses, and low-level fighting continued until Saddam's overthrow in 2003.