“The sheer scale of violence shocked the international community, yet the world’s leading powers secretly aided and abetted the two factions.”

THE EIGHT-YEAR conflict between Iran and Iraq was the bloodiest of the 1980s and the longest running interstate war of the 20th Century.

As many as a million perished in the fighting, which targeted both military personnel and civilians alike. It was a war that saw vast armies collide on the battlefield as bombs, missiles and chemical weapons rained down on cities filled with non-combatants.

The sheer scale of violence shocked the international community, yet the world’s leading powers secretly aided and abetted the two factions. And when it was over, the Persian Gulf was left in a state of turmoil that would keep the Western powers involved there for decades.

Here are 10 essential facts about the Iran-Iraq War; how it started, how it was fought and how it left the region scared for a generation.

The war was years in the making

Tensions between Iran and Iraq were longstanding. Among the many issues that gave rise to the conflict was control of the Shatt al-Arab waterway, a vital shipping route that links the Euphrates and the Tigris rivers with the Persian Gulf. Along its banks sits the Iranian cities of Abadan and Khorramshahr and the Iraqi port of Basra. After decades of bickering over who could access its deep waters, an agreement was reached in 1975 that promised to finally resolve the issue.

Unfortunately, the compromise was upended in 1979 following the Iranian Revolution, which saw the U.S.-backed Shah of Iran toppled by Islamic fundamentalists. Iraq’s dictator Saddam Hussein was a sworn enemy of Iran’s new supreme religious leader, the Ayatollah Khomeini. After being exiled from Iran in the 1960s, the radical Iranian cleric settled in Najaf, Iraq where he would sow dissent among Saddam’s own majority Shia population. In 1978, Baghdad finally ordered Khomeini expelled. The following year, the Ayatollah took power in Iran and continued calls for the ouster of Iraq’s Ba’athist regime. Skirmishes soon erupted along the Shatt al-Arab. Finally, on Sept. 22, 1980, Saddam ordered an all-out invasion of Iran.

The armies were mismatched

Although Iran had roughly three times the land and population of Iraq, Saddam’s Soviet-equipped army dwarfed the opposition. Iraq could field 200,000 troops, along with nearly 7,000 armoured vehicles and 1,400 guns. Iran had half as many men, tanks and artillery. But what it lacked in numbers, it would make up for with religious zeal. New York Times correspondent John Kifner characterized Iran’s army in 1982 as “a curious military force of professional soldiers, mullahs, neighbourhood militiamen and schoolboys as young as 13, linked by an intense Islamic fervour.”

It began with a surprise attack

Iran enjoyed one considerable advantage over Iraq. As a one-time ally of Washington and the West, it had hundreds of top-of-the-line, U.S.-built fighter interceptors, including nearly 80 brand-new Grumman F-14 Tomcats. Saddam’s generals gambled that a pre-emptive surprise attack on Iran’s air fields in the opening minutes of hostilities would catch these formidable warplanes on the tarmac. So, on Sept. 22, 1980, squadrons of Iraqi MiG-23s, Su-20s and Tu-22 bombers penetrated Iranian airspace without warning and hit a dozen air bases across the country, including one just outside the capital of Tehran. The airstrikes were followed by a three-pronged ground offensive by the Iraqi army along a 400-mile front. The objective was to seize vast areas of western Iran, which it was hoped would precipitate the downfall of the Khomeini regime.

Despite catching the Iranian air force entirely off guard, the air raids inflicted only light damage. In fact, many of the prized American-built warplanes were safe inside concrete bunkers at the time of the attack. Then Iran hit back.

Just a day after the Iraqi raids, 160 Iranian F-4 Phantoms and F-5 Tigers bombed 11 airfields inside Iraq, including the “super base” of Muthenna, and even Baghdad International Airport. The attack, codenamed Operation Kaman 99, was devastating. A number of major Iraqi runways were put out of action for months and, according to some estimates, the capability of Saddam’s air force was cut by nearly half.

It quickly deteriorated into a WW1-style stalemate

In the opening days of the war, Iraqi forces pushed miles into the Iranian province of Khuzestan. Yet within weeks, their advance stalled as Iranian resistance stiffened. The fighting soon bogged down into a deadly stalemate. As the lines stabilized, the conflict morphed into a bloody, high-tech rerun of the First World War’s Western Front. Trenches, barbed wire and machine gun nests divided the opposing armies as both sides dug in rather than expose their troops and armoured vehicles to enemy fire. Bayonet charges, massed artillery bombardments and even poison gas attacks further fuelled comparisons with the Somme or Verdun. The deadlock, which continued for years, was punctuated by massive offensives and counter attacks. Pitched and bloody battles were fought in places like Dezful, Khorramshahr, al-Faw and Mehran. The body count began to climb.

Iran’s “human wave” attacks horrified the world

Unable to match Iraq’s sizeable Soviet-equipped army, Iran planned to overwhelm the invaders with massed 1,000-man light infantry attacks. Known as “human waves,” these typically involved large-scale frontal assaults on enemy positions by raw Basij paramilitary volunteers. Predictably, the casualties were horrendous. Despite the shocking death tolls, the charges were not the mindless slaughters that were widely reported in the international press. The attacking troops were often split into small 20-man squads, each with a specific target or objective to capture. Assaults were carried out at night, in many cases. Infiltration, surprise and deception tactics were routinely employed. Once the teams had blown open gaps in the enemy defences, fresh reinforcements from the professional army would be rushed forward exploit the breaches.

Unable to withstand the ceaseless ground assaults, Saddam pulled his depleted army back to the border in 1982. Baghdad called for a ceasefire and peace talks. Iran refused and instead invaded Iraq. Its victorious armies surrounded the city of Basra in what would become one of the largest land battles since the Second World War.

Civilians were in the crosshairs

With the tide turning against him, Saddam sought to force Tehran to the peace-table with a terror campaign that targeted Iranian civilians. Iraqi warplanes shot down civilian jet liners and strafed passenger trains. In one October, 1986 incident, a 737 full of air travellers was bombed on a runway at Shiraz. That same year, Baghdad ordered raids and Scud missile strikes on more than 60 Iranian population centres in what would become known as the “War of the Cities.” In one attack, 65 Iranian children died as a missile hit a primary school in Borujerd. Tehran retaliated with its own missile campaign. And that wasn’t the end of the atrocities. As early as 1983, Saddam opened a new front against rebellious Kurds in northern Iraq. The violence, which was ruthlessly indiscriminate, culminated in 1988 with the Halabja massacre, an infamous genocidal nerve and mustard gas attack on Kurdish civilians that left 5,000 dead.

The war made for some strange political bedfellows

The conflict marked a rare occasion in which the United States and the Soviet Union shared a common ally. Iraq had long been a Cold War partner of Moscow. But with a violently anti-American revolutionary regime in power in Tehran, Washington found itself supporting Baghdad too. Not only did the U.S. provide money and intelligence to the Iraqi dictator, in 1982, President Reagan announced that Iran’s defeat in the war was an official American foreign policy goal. Ironically, just four years later, the White House would be discovered secretly selling weapons to Iran, in direct violation of its own arms embargo. The clandestine transactions were carried out to raise money for anti-communist guerrillas in Nicaragua. What would become known as the Iran-Contra scandal eventually threatened to bring down the Reagan presidency.

It threatened to escalate into a regional conflict

Desperate to bring foreign powers into the conflict, Saddam deliberately expanded the fighting into the international shipping lanes of the Persian Gulf. The Iraqi dictator bet that by targeting Iranian tankers and the ships of his enemy’s trading partners, Tehran would retaliate in kind. The resulting chaos would disrupt the flow of oil from the region and draw other nations into the conflict on the side of Baghdad. As predicted, Iran responded in kind, firing on Iraq’s oil tankers along with Kuwaiti and Saudi vessels carrying Iraqi petroleum. Ultimately, both sides would damage more than 500 ships from various nations. In one 1987 incident, an Iraqi Mirage fighter launched two French-made Exocet missiles at a target it believed to be an enemy vessel. It was in fact the American destroyer USS Stark. Nearly 40 of the ship’s crew died. Washington was quick to accept its ally’s apology. As missile and small boat attacks intensified that summer, Tehran threatened to close the Straits of Hormuz. The United States responded by dispatching a naval task force to the region to escort U.S.-flagged international tankers in and out of the Persian Gulf. America and Iran traded fire in a number of incidents, but the outbreak of general hostilities was avoided.

Fighting continued even after the armistice

By the spring of 1988, both sides were exhausted politically, economically and militarily. On the frontlines, Iran had suffered an epic defeat at the gates of the Iraqi city of Basra. Meanwhile at home, sanctions were strangling the country’s economy. Iran’s army was all but out of volunteers and desertions were up. All the while, the revolutionary regime feared that the United States might enter the war. Iraq was in somewhat better shape, but it was still buckling under the strain of an eight-year campaign that was costing its treasury billions of dollars every month. Enemy troops were dug in on Iraqi soil and Baghdad faced an ongoing Kurdish insurgency within its own borders.

Saddam gambled that one more round of missile strikes on Iranian cities, along with threats to launch chemical weapons into the capital, would finally force the enemy to the negotiating table. On July 20, 1988, Tehran agreed to the terms of UN Resolution 598, which called on both sides to suspend hostilities and withdraw to pre-war boundaries. Baghdad also signed on. Yet only days into the ceasefire, Saddam would make one final attempt to overthrow Iran’s fundamentalist leadership.

On July 26, an army of Iranian ex-pat insurgents sheltering in Iraq known as Mojahedin-e Khalq invaded their homeland. The Revolutionary Army swiftly crushed the guerrillas. Sporadic clashes continued for weeks after the ceasefire; Iran continued to fire on Iraqi shipping and Saddam even ordered gas attacks on Iranian cities. Yet caving to international pressure, both sides suspended hostilities entirely in time for the first UN Peacekeepers to arrive on Aug. 20.

It set the stage for future conflicts

In the aftermath of the fighting, both Iran and Iraq found themselves in precarious positions.

Tehran was militarily depleted, economically bankrupt and politically isolated. Yet the regime had succeeded in driving the invaders from its soil and would survive. For its part, Iraq emerged from the struggle as a virtual pariah on the world stage. Despite earlier support from Western governments, the international community had recoiled from the country’s indiscriminate use of chemical weapons and its brutal suppression of the Kurds. And although his military was the fifth largest on the planet, Saddam owed billions to his neighbours and his war-ravaged economy was dangerously susceptible to fluctuations in the global price of oil.

Just two years after the ceasefire, Iraq invaded its neighbour Kuwait. Baghdad had long claimed the territory as its own and now the tiny emirate’s overproduction of oil was driving down the price of petroleum, which threatened to harm Iraq’s already struggling economy. In 1991, an international coalition drove Saddam’s army out of Kuwait. Crippling sanctions and new rounds of air strikes kept the Iraqi dictator contained for years. The 2003 U.S.-led invasion of Iraq would finally bring down the country’s Ba’athist government; years of sectarian turmoil followed. That, along with the civil war in neighbouring Syria, would ultimately give rise to the Islamic State.