Iran-Iraq War, 1980–88, protracted military conflict between Iran and Iraq. It officially began on Sept. 22, 1980, with an Iraqi land and air invasion of western Iran, although Iraqi spokespersons maintained that Iran had been engaging in artillery attacks on Iraqi towns since Sept. 4. Iraqi president Saddam Hussein claimed as the reason for his attack on Iran a territorial dispute over the Shatt al Arab, a waterway that empties into the Persian Gulf and forms the boundary between Iran and Iraq. In 1975, a militarily weaker Iraq had by treaty signed over to Iran partial control of the waterway, but after the fall (1979) of Muhammad Reza Shah Pahlevi and the resultant weakening of Iran's military, Iraq seized the opportunity to reclaim the Shatt al Arab. Iraq also hoped to seize the western Iranian region of Khuzestan, an area known for its extensive oil fields. The Iraqi offensive was initially successful, capturing the port city of Khorramshahr by the end of 1980. Iranian resistance proved strong, however, and Iraqi troops had withdrawn from the occupied portions of Iran by early 1982. Nevertheless, Iranian leader Ruhollah Khomeini declared that Iran would not cease fighting until Saddam's regime was toppled. Iran began a series of offensives, which proved successful enough to cause Iraq to resort to the use of chemical weapons (see poison gas), a tactic reviled by the international community. Iranian troops captured the oil-rich Majnoon Islands from Iraq in Feb., 1984, and southern Iraq's Fao peninsula in early 1986. Sporadic air and missile attacks on cities and military installations were common throughout the war, and in 1985 both sides began to strike their opponent's capital. The United States and several Western European nations became involved in the war in 1987, in response to Iranian attacks on Kuwaiti oil tankers traveling in the Persian Gulf. These attacks sullied Iran's international reputation considerably, making it difficult for Khomeini to obtain arms. Finally, in July, 1988, Iran was forced to accept a United Nations–mandated cease-fire. Estimates of the number of dead range up to 1.5 million. In its war effort, Iran was supported by Syria and Libya, and received much of its weaponry from North Korea and China, as well as from covert arms transactions from the United States. Iraq enjoyed much wider support, both among Arab and Western nations: the Soviet Union was its largest supplier of arms. In 1990 Iraq, concerned with securing its forcible annexation of Kuwait (see Persian Gulf War), agreed to accept the terms of the 1975 treaty with Iran and withdraw its troops from Iranian territory as well as exchange all prisoners of war. An agreement was not signed, however, and both sides held thousands of POWs for many years. Several prisoner exchanges and releases occurred after 1988; the final exchange took place in 2003.