The Syrian government has used chemical weapons, including sarin nerve agent, against rebel fighters “multiple times in the last year,” the U.S. intelligence community has concluded. The attacks killed at least 100 people, White House spokesman Ben Rhodes said Thursday.

“The use of chemical weapons violates international norms and crosses clear red lines that have existed within the international community for decades,” Rhodes said. But the Syrian gas attacks were hardly the first use of chemical agents in modern warfare. Conflicts in Iran, Iraq and Yemen in the last 50 years have also involved chemical attacks resulting in thousands of deaths. Even the U.S. has used munitions that some critics say should be classified as chemical weapons.

Yemeni royalists in 1962. Via Wikimedia Commons

Yemen

Poisonous gas was a lethal fixture on World War I battlefields but was probably not used in World War II. Chemical weapons made a comeback during the Cold War. Soviet-backed Egypt is believed to have deployed chemical weapons (CW) — reportedly including phosgene and mustard — in its fighting against Western-supported Yemeni royalists in the 1960s.

“Varying explanations for Egypt’s use of CW agents in Yemen have been offered,” the nonprofit Nuclear Threat Initiative explained. “These include the suggestion that CW agents were considered an effective weapon against tribesmen hiding in caves; the expectation that Yemen might be a good testing ground for such weapons; and the possibility that Egyptian forces simply wanted to take advantage of a weapon in their arsenal which their had no protection against.”

As many as 1,500 royalists died in the attacks.

Egypt is a signatory to the 1928 Geneva Protocol, which bans chemical weapons — but that didn’t stop Cairo from gassing the Yemenis. And Egypt never signed the more recent Chemical Weapons Convention.

Victims of the Sardasht attack. Via Wikimedia Commons

Iran

Baghdad unleashed frequent, massive and devastating chemical attacks on Iranian troops during the 1980-1988 Iran-Iraq war. On June 28, 1987, Iraqi warplanes dropped mustard gas canisters on the Iranian town of Sardasht.

Nine thousand people were exposed. Around 130 died. “The victims gasped and vomited on rusting buses as they were rushed to hospitals,” The Los Angeles Times reported. “They dropped dead on the cobbled streets of the town center. They cried out as their eyes burned and skin bubbled.”

Iran appealed to the U.N. but the world body reportedly had little patience for the Islamic regime’s protestations. Embargoes prevented Iran from acquiring gas masks and other defenses. Being all alone on the receiving end of chemical warfare taught the Iranians “that they cannot rely on the international law for justice, or on the international community to come to their assistance in the darkest hour,” wrote Jean Pascal Zanders from the Bulletin of Atomic Scientists.

Gravestones of Halabja victims. David Axe photo

Iraq

After the war with Iran, Iraq aimed its chemical weapons at its own people. On March 16, 1989, Iraqi jets spread a cocktail of lethal gases over Halabja, a town in the breakaway Kurdish northern region.

At first residents feared a conventional bombing and crowded into claustrophobic bunkers. “When they realized it was a chemical attack they tried to get out,” one survivor recalled, “but most of them died in their shelters.”

Five thousand people died and the rebuilt Halabja became a symbol of Kurdish resistance. Survivors and their descendants continue to suffer high rates of cancer and other diseases and disorders.

In making the case for the 2003 invasion of Iraq, U.S. official pointed to Halabja as proof that Saddam Hussein’s regime was capable of using Weapons of Mass Destruction and should be destroyed.

An Army OH-58D fires rockets in Afghanistan.Army photo

Vietnam, Iraq and Afghanistan

The United States has signed all the major treaties banning chemical weapons but is not totally innocent of using controversial chemical agents in wartime.

American planes sprayed tree-killing Agent Orange over a quarter of southern Vietnam in the 1960s and ‘70s. Agent Orange included dioxin, which lingered in the environment and according to the Aspen Institute “is still causing health problems in Vietnam.” And in American veterans.

Moreover, U.S. warplanes, helicopters and artillery have fired white phosphorous munitions in Iraq and Afghanistan. Technically a smoke-generating “obscurant,” the incendiary qualities of white phosphorous have led to calls for banning the substance.

An eight-year-old Afghan girl named Razia was caught in an apparent U.S. white phosphorous barrage in 2009. “When she reached the operating room, white powder covered her skin, the oxygen mask on her face started to melt, and flames appeared when doctors attempted to scrape away the dead tissue,” Human Rights Watch noted.

“The president has been clear that the use of chemical weapons … is a red line for the United States,” Rhodes said Thursday. But it’s a red line that many nations have crossed, possibly including the U.S.