The rise of an Islamic republic in the Shia-majority Iran under Khomeini in early 1979 provoked militancy among Iraqi Shias, to the extent that the increasingly powerful first vice president of the republic, young Saddam Hussein, a Sunni, acted severely against them, much to the unease of the oder President Bakr.  While Khomeini took to appealing to Iraqis to overthrow the "non-Muslim" Baathist regime, Baghdad encouraged the ethnic Arabs in the oil-rich Iranian province of Khuzestan to demand autonomy and sabotage oil installations.  The differences between Bakr and Saddam on how to tackle the Shia problem became irreconcilable.  So on July 17, 1979, the eleventh anniversary of the Baathist seizure of power, Saddam Hussein became chairman of the Revolutionary Command Council and president of Iraq after forcing Bakr to step down.

On the fifth anniversary of the 1975 Iran-Iraq treaty of International Boundaries and Neighborliness, Saddam declared in the newly convened Parliament that he was abrogating the treaty forthwith.

This was the prelude to the Iraqi invasion of Iran.

The Iran-Iraq War

On September 22, 1980, Iraq invaded Iran, a country three-and-a-half times as large and four times more populous than itself.  Its army crossed the border at several points while its air force bombed Iranian military installations and economic targets.  Angered by the Iranians' hostage-taking at the US embassy in Tehran in November 1979, the Carter administration had encouraged Iraq, through diplomatic back channels, to attack Iran.  Now, however, Washington declared itself neutral in the war.