September 22, 1980: Iraq invaded Iran, launching an 8-year war that killed 500,000 to 1 million people—one of the deadliest conflicts since World War II.

The U.S. supplied Saddam Hussein's military with targeting intelligence throughout the conflict. Two-thirds of Iraq's chemical weapons attacks occurred in the final 18 months, when CIA-Iraq coordination peaked.

NATO countries provided Iraq with dual-use technology and precursor chemicals used to manufacture chemical agents deployed against Iranian forces.