Iraq once devastated Iran with chemical weapons as the world stood by. Governments still struggle to respond to chemical warfare

In April 1915, the German army tried a new tactic to break through allied trenches on the front lines of World War I: the first large-scale use of poison gas. It was a devastating attack on the unprepared allies, and as the heavier-than-air chlorine gas cloud passed over their lines, 1,100 unprotected soldiers died and others retreated, hacking and desperate for air. Although the Germans were slow to press their advantage, the gas had its intended effect and cleared miles of trenches where allied troops had previously stood guard.

Although successful on the surface, the gas attack at the Second Battle of Ypres, a city in Belgium, also highlighted the operational drawbacks of chemical weapons. Targeting an adversary with a weapon that can be dispersed by the whim of the weather and having it reach a target in sufficient quantities without blowing back on the attacking forces is no simple matter. It requires careful observation of the winds and precise placement of the weapons. At Ypres, chemist and future Nobel Prize-winner Fritz Haber, who had advocated for Germany’s use of the poison gas, was personally on hand to manage the placement of thousands of gas canisters. When the allies followed Germany’s example and began engaging in chemical warfare themselves, the overall effect was mixed. At the Battle of Loos, about six months after Ypres, a British chlorine gas attack blew back on the attackers.

Many countries, including the United States and Russia, once maintained large chemical weapons arsenals. A global treaty banning them went into effect in 1997, but it hasn’t stopped rogue governments from continuing to resort to their use, despite a prevailing argument that chemical weapons do not provide a strategic advantage in shaping the outcomes of wars. Yes, the unconventional weapons can undermine troop morale and cause panic among civilian populations, researchers say. But overall, the consensus is that they do not offer strategic benefits. They cannot destroy military equipment. They can be defended against using countermeasures, including gas masks and other protective gear. And weather and climate conditions affect their reliable use. Each of these factors make them undesirable from the perspective of military effectiveness.

Militaries have used chemical weapons in more than a dozen civil and international conflicts, yet they have not generally secured decisive victories or profoundly changed the course of those conflicts. There is one war, however, that complicates the conventional wisdom on chemical weapons: the protracted Iran-Iraq War. In that conflict, chemical weapons were arguably decisive in allowing Iraq to reclaim the upper hand in the conflict and forcing Iran to agree to the UN resolution to bring an end to the war.

The Iran-Iraq War. On September 22, 1980, Iraq launched an extensive attack on Iran, igniting a devastating eight years of war. Saddam Hussein, the authoritarian president of Iraq, was driven by a combination of opportunity and fear: the opportunity to achieve geopolitical gains amidst Iran’s internal turmoil following the 1979 revolution (particularly, to assert control over the entire Shatt al-Arab, the border river between the two countries), and the fear of potential destabilization of his regime from spillover effects from the Iranian revolution. The initial offensive involved airstrikes targeting crucial infrastructure, quickly followed by a ground invasion that led to the swift capture of several western Iranian cities. The attack plunged both nations into a war with immense suffering and economic devastation. In general, the conflict itself can be categorized as having three main phases: the early war period (1980-1982), when Iraq held the advantage; the mid-war period (1982-1986), featuring a robust Iranian counteroffensive; and the late war period (1986-1988), which culminated in a stalemate and eventual resolution. During each of these periods, Iraq’s strategic use of chemical weapons evolved.

In the early period, Iraqi forces made significant territorial gains, capturing key Iranian cities and infrastructure. At this time, Iran was on the defensive, a country still grappling with internal strife between political groups following the 1979 revolution. The Islamic Republic was in its nascent stage, still consolidating power and establishing its governance structures. Iraq’s use of chemical weapons in this period was sporadic and experimental, not yet a central pillar of its war strategy.

After early successes, however, the Iraqi invasion stalled and was then repelled. By 1982, Iran had recaptured almost all of its territories In June of that year, following the near-total expulsion of Iraqi forces from Iranian soil, the Iraqi government proposed a ceasefire. The Iranian leadership declined the offer, arguing that the aggressor, Saddam Hussein, needed to be punished and make reparations for the invasion.

In the second phase of the war, Iran regained momentum through a series of successful counteroffensives. Strengthened by a surge of volunteer fighters and improved logistical coordination, the Iranian military reclaimed much of the territory lost to Iraq. And it was in this period of Iranian momentum, that Iraq began its systematic and extensive use of chemical weapons. To diminish Iran’s manpower advantage, the Iraqi military bombarded troops with mustard gas to disrupt Iran’s ability to use mass infantry assaults.

As the situation grew more dire for Iraq, Hussein’s use of chemical weapons increased. On March 10, 1986, Iranian forces achieved a significant milestone, capturing the al-Faw Peninsula, and pushing toward Basra, a strategically important city. Over the course of the conflict, Iraq not only increased the quantity of chemical weapons deployed but also their lethality, progressively incorporating more potent agents into its arsenal.

Data from Persian sources and books authored by Mohammad-Bagher Nikkhah-e Bahrami (The Chronology of Iraqi Chemical Attacks in the Eight Year Iran-Iraq War and War Crime: Iraq’s Chemical Attacks in War against Iran) show a marked escalation in Iraq’s employment of the most lethal chemical weapons, such as blood and nerve agents, reflecting a deliberate intensification of chemical warfare tactics as the war progressed.

New tactics and a new threat. Two significant developments occurred toward the end of the war, particularly from 1987 onwards. First, as Iranian troops enhanced their chemical defenses, Iraq shifted its focus towards targeting civilian populations. This strategy was aimed at demoralizing civilians and increasing pressure on Iranian leadership. In June 1987, the Iraqi Air Force launched an aerial attack using mustard gas and possibly nerve agents on the town of Sardasht. This attack killed 130 people and chemically injured 8,000, marking the first time in history that chemical weapons were explicitly directed at a purely civilian population. However, this was only a precursor to the horrors that would follow. Nine months later, in March 1988, Hussein’s forces executed a devastating chemical attack against the Kurdish civilian population in Halabja, in Iraqi Kurdistan. This attack—part of a campaign against Kurdish rebels who had allied with Iran—was the largest chemical weapons attack directed against a civilian-populated area in history. The assault killed approximately 5,000 people and left many more injured or with long-term health problems. In this last phase of the war, Iraq would carry out a total of 30 chemical attacks on civilian population centers.

In addition to the toll the attacks were taking on troops and civilians, another factor loomed large in the minds of Iran’s leaders. Iraq, in addition to developing chemical weapons tactics and expanding its arsenal, had also been improving the range of its missiles. At the start of the war, Iraq’s missiles had range of 70 kilometers, only long enough to strike border towns. But by 1987 Iraq had achieved a significant breakthrough in its missile technology, developing the Al-Hussein missile, an extended-range variant of the Soviet-made Scud-B, which could travel up to 650 kilometers. Starting in February 1988, Iraq launched a total of 164 of the missiles at key Iranian cities, including Esfahan, Shiraz, Tabriz, Qom, and, most importantly, Tehran. Now Iraq had the willingness and capacity to threaten Iran’s densely populated cities, including its capital, with chemical weapons attacks.

During the final stage of the war, the use of chemical weapons played a crucial role. From April to July of 1988, Iraq mounted a series of decisive counteroffensives during which it reclaimed its previously lost territories, including the strategically crucial al-Faw Peninsula. During this period, Iraq escalated its use of the weapons, deploying deadly nerve and blood agents in an aggressive bid to regain territory. These chemical attacks, combined with Iraq’s renewed manpower, which vastly outnumbered diminished Iranian forces, proved devastatingly effective. The overwhelming force and use of chemical warfare rapidly collapsed the Iranian defensive lines. Iraq managed to recapture the al-Faw Peninsula in just 36 hours and regained all territories lost since 1983 within four months.

A surprising ceasefire. Iranian leadership had consistently opposed any compromise to end the war, insisting that UN Security Council resolutions explicitly recognize Iraq as the initiator of the conflict. When the United Nations Security Council on July 1987 passed the resolution 598 calling for an immediate ceasefire between the two countries, Iran initially resisted its terms. The resolution failed to explicitly name Iraq as the aggressor. However, a surprising shift occurred a year later, when Iran accepted the resolution. At the highest levels, the Iranian government had long vowed to press on until the collapse of Saddam Hussein’s government.

A detailed review of interviews and documents released in the years following the war indicates that Iraq’s deployment of chemical weapons was a pivotal factor influencing Iran’s decision-making process. The most insightful information comes from one central figure’s extensive documentation regarding wartime decision-making. Hashemi Rafsanjani was at points the speaker of the parliament and Ayatollah Khomeini’s representative on the Supreme Defense Council. In 1988, Rafsanjani was the acting commander-in-chief of the Iranian armed forces. In particular, he played a key role in persuading Khomeini, the leader of the Islamic Republic, to accept the UN ceasefire resolution.

According to Rafsanjani, Iraq’s bombardment of Kurdish rebels strongly influenced ceasefire deliberations in Iran. He noted that even the Revolutionary Guard leaders, who had been staunchly resilient throughout the war, exhibited signs of fear following the Halabja tragedy. Rafsanjani stated, “The Iraqis showed in Halabja that if tomorrow they were to strike Tabriz in the same way, there would be nothing we could do about it.” This concern about the potential for chemical attacks on major Iranian cities recurs throughout Rafsanjani’s interviews. His concern was well-founded. Saddam Hussein had sent a message through several Arab countries to Iran, warning that if Iran did not agree to end the war, Iraq would deploy weapons that Iranians had never even considered. Many interpreted this as a threat of chemical attacks on densely populated cities like Tehran.

Recognizing the dire situation, the heads of the three branches of government, along with then Prime Minister Mir-Hossein Mousavi and Ahmad Khomeini (Ayatollah Khomeini’s son and chief of staff), agreed to seek diplomatic solutions. They aimed to persuade the UN Security Council to acknowledge Iran’s demands (recognizing Iraq as the aggressor) and to discuss the country’s precarious circumstances with Ayatollah Khomeini. By that point, public enthusiasm for the war in Iran, once a major driving force, had significantly waned after eight long years, making further mobilization a daunting challenge.

Ayatollah Khomeini, who ultimately made the final decision to end the war, articulated his rationale in a letter addressed to the authorities of the Islamic Republic. He conveyed that military officials had openly admitted the unlikelihood of securing a swift victory. Furthermore, he noted that both military and political leaders had reached a consensus that prolonging the war was detrimental to the nation’s best interests. Importantly, he highlighted the pivotal issue: “the enemy’s extensive use of chemical weapons and our inability to neutralize them,” which ultimately compelled him to agree to the ceasefire.

International response. Throughout the conflict, Iraq’s use of chemical weapons was a blatant violation of the Geneva Protocol of 1925, which prohibits the use of chemical and biological weapons in war. Despite these violations, the response from the international community, including the UN Security Council, was tepid and inconsistent. This lack of decisive action was mainly due to the geopolitical dynamics of the time. Iraq was seen by many Western powers, including the United States, as a counterbalance to the revolutionary government in Iran.

In 1983, when Iraq extensively used chemical weapons for the first time, UN Secretary-General Javier Pérez de Cuéllar dispatched a team of specialists to Iran to investigate the allegations; they confirmed the use of chemical weapons. While the secretary-general’s report acknowledged the aerial bombing with chemical weapons against Iranian forces, it stopped short of attributing responsibility to Iraq. In subsequent years, the Security Council voiced its dismay over the use of chemical weapons, explicitly stating in 1984 and again in 1985 that it was “appalled that chemical weapons have been used against Iranian soldiers during the month of March 1985.”

Nonetheless, the council’s statements merely urged “both parties to observe the generally recognized principles and rules of international humanitarian law” without specifically naming the perpetrator. The issue of chemical weapons did not appear in Security Council resolutions until February 1986, when Resolution 582 explicitly condemned their use—yet refrained from naming Iraq as the responsible party. It was only in March 1986 that the Security Council mentioned Iraq in a declaration (not a resolution) expressing “profound concern by the unanimous conclusion of the specialists that chemical weapons on many occasions have been used by Iraqi forces against Iranian forces.” Even so, the Security Council failed to explicitly name Iraq as the responsible party in any of its resolutions from 1986 to 1988. This is important because resolutions carry more legal weight than declarations.

The US role in facilitating Iraq’s chemical warfare campaign is now well-acknowledged. Declassified documents and interviews with former officials have revealed that the United States was not only aware of Iraq’s chemical attacks but actively provided intelligence support to Hussein’s regime. This support, driven by the geopolitical goal of countering Iranian influence, included detailed imagery and maps of Iranian troop movements, logistical facilities, and air defenses. This intelligence was instrumental in Iraq’s ability to plan and execute severe chemical attacks, particularly during the final stages of the war in 1988.

The general silence and passivity of the international community likely emboldened Hussein, indicating that he could continue his chemical campaign with virtually no fear of significant international consequences.

A chemical legacy. Iran’s decision to end the war was influenced by a combination of critical factors. These included dwindling human resources and volunteers, growing economic challenges, enhanced Iraqi military capabilities that shifted the balance of power, and an increasing US military presence in the Persian Gulf, which was perceived by Iran, at the time, as support for Iraq. However, the use of chemical weapons against civilians, particularly the attack on Halabja, emerged as a decisive factor in tipping the scales towards accepting the UN ceasefire resolution and ending the war.

These attacks had a profound impact on the conflict’s progression and resolution. The psychological and operational effects of chemical weapons significantly weakened Iranian forces and morale. More critically, the targeting of civilians affected the decision calculus of Iran’s elite. This underscores the need for a nuanced understanding of the role of chemical weapons in warfare, recognizing both their limitations and their potential to shape military and political outcomes in specific contexts.

The effective use of chemical weapons during the war and the tepid response from individual countries and the United Nations in regard to Iraq’s repeated violations of international law highlight the limitations of global arms-control agreements and norms meant to halt the use of weapons. These limitations are further underscored by recent instances of chemical weapons use in the Syrian civil war and the Ukraine-Russia conflict despite strong condemnations from the international community. Efforts to reinforce norms against chemical weapons through the Chemical Weapons Convention (CWC) have been ongoing since 1993, yet governments continue to avoid being held accountable for their actions.