Iran–Iraq War

The Iran–Iraq War, also called the First Imposed War, Eight-Year War, or Sacred Defense by Iran, began with the Iraqi invasion of Iran in September 1980. After eight years of conflict, both countries accepted a ceasefire deal brokered by the United Nations, which became effective in August 1988. The war caused around 500,000 deaths (excluding numbers from the related Anfal campaign), making it the deadliest conventional war ever fought between regular armies of developing countries.

In starting the war, the Iraqi government—led by President Saddam Hussein—primarily wanted to prevent Ruhollah Khomeini, Iran's leader following the 1979 Iranian Revolution, from exporting Iran's new state ideology to Iraq. Iraq also feared that Iran, being a theocratic state mostly composed of Shia Muslims, would rally Iraq's Shia majority against the Sunni Muslim-controlled Baʽathist government. Iraq also wished to replace Iran as the main national power in the Persian Gulf. The war followed a long-running history of border disputes between the two states, as a result of which Iraq planned to retake the eastern bank of the Shatt al-Arab river that it had ceded to Iran in the 1975 Algiers Agreement.

The conflict involved large-scale trench warfare, and deliberate attacks on civilians, including Iraqi chemical attacks. At the start of the war, Iraq expected a decisive victory, considering Iran's post-revolutionary chaos, but their invasion had stalled by December 1980. The Iranian military then gained momentum, and recaptured all their territory by June 1982. Having pushed Iraqi forces back to the pre-war borders, Iran launched an invasion of Iraq, which created a five-year offensive. In mid-1988, Iraq launched a series of counter-offensives that created the military stalemate present at the war's end.

Iraq was aided by the National Council of Resistance of Iran, the United States, the United Kingdom, the Soviet Union, France, Italy, Yugoslavia, and most Arab countries. Iran was aided by the Kurdistan Democratic Party, the Patriotic Union of Kurdistan, Syria, Libya, North Korea, China, South Yemen, Pakistan, Cuba, and Israel. Meanwhile, Iraqi support for Arab separatists in Iran increased.

After years of military and economic losses, decreasing morale, intensifying Iran–U.S. relations, and little international action against Iraqi attacks on Iranian civilians, Iran agreed to a ceasefire with Iraq under United Nations Security Council Resolution 598. The war did not create any permanent border changes, and neither country received war reparations afterwards. Both sides suffered financially. They continued engaging in low-level military conflict until relations improved following Saddam's overthrow in 2003.