Chemical Weapons: History and Modern Threats

Few categories of weapons provoke as much horror as chemical weapons. The image of soldiers choking in the trenches of World War I, or families collapsing in their homes during a gas attack, has shaped how the world views these arms for over a century. Yet the story of chemical warfare stretches far beyond the modern battlefield. It runs from ancient sieges to Cold War stockpiles, and from sweeping disarmament treaties to disturbing reminders that the threat has not fully disappeared. Understanding this history is essential to grasping why chemical weapons remain a central concern in the study of weapons of mass destruction.

What are chemical weapons? 🔗

A chemical weapon uses the toxic properties of chemical substances to kill, injure, or incapacitate people. Unlike conventional explosives that rely on blast and fragments, these weapons attack the body directly through inhalation or skin contact, often producing immediate and agonising effects. Their indiscriminate nature means they harm soldiers and civilians alike, which is a major reason they are treated as a separate, especially abhorrent category of weaponry.

The main types of chemical agents 🔗

Chemical agents are usually grouped by how they affect the human body. The four broad classes are:

• Nerve agents: Substances like sarin, tabun, and VX. A tiny amount of sarin can kill within minutes by blocking acetylcholinesterase, an enzyme needed to transmit nerve signals.
• Blister agents: Mustard gas is the best-known example. It burns the skin, eyes, and respiratory tract, causing painful blisters.
• Choking agents: Chlorine, phosgene, and similar gases that damage the lungs and cause victims to suffocate.
• Blood agents: Compounds such as hydrogen cyanide that interfere with the body’s ability to use oxygen.

An ancient practice, not a modern invention 🔗

While we tend to associate chemical warfare with the 20th century, the use of poison and noxious smoke in battle is thousands of years old. Ancient Chinese forces are said to have used bellows to pump arsenic fumes toward their enemies, with such accounts dating back well over two thousand years. The principle was crude but effective: make the air itself a weapon.

One of the earliest documented cases comes from Greece. During the siege of Plataea in 429 BC, Spartan soldiers burned sulphur and pitch to release toxic clouds over the defenders, forcing them to abandon their positions. Centuries later, evidence from the Roman city of Dura-Europos in modern Syria suggests that Persian attackers used burning sulphur and bitumen to trap and suffocate Roman soldiers in a tunnel. Interestingly, the very idea that poison was a dishonourable, cowardly tactic also has deep roots, with some scholars tracing the sentiment back to ancient Indian epics and Greek mythology.

For all these examples, a key limitation held the practice back for millennia. Without advanced industry, no army could reliably manufacture or stockpile chemical agents in significant quantities. That changed dramatically with the Industrial Revolution.

World War I: chemical warfare goes industrial 🔗

The First World War marked the true beginning of modern chemical warfare. Industrial chemistry made it possible to produce poison gases on a massive scale. The early use was relatively limited; French troops first loaded tear gas into hand-thrown grenades to flush German soldiers from their trenches.

The conflict escalated quickly. On 22 April 1915, German forces released chlorine gas from thousands of cylinders along a six-kilometre front at Ypres, Belgium. The wind-borne cloud opened a major gap in the lines of unprepared French and Algerian units. This is widely regarded as the first large-scale use of a chemical weapon as a tool of mass destruction. Soon both sides were deploying chlorine, phosgene, and the dreaded mustard gas.

The human cost was staggering. Across the war, gas warfare caused more than one million casualties and killed roughly 90,000 people. The German chemist Fritz Haber, who oversaw Germany’s gas programme, is often grimly remembered as the “father of chemical warfare.” The sight of victims gasping and choking left a deep moral scar on the world and created lasting public revulsion.

The first attempt to ban: the Geneva Protocol of 1925 🔗

The horror of gas warfare led directly to the first major international response. The 1925 Geneva Protocol prohibited the use of asphyxiating, poisonous, and other gases, as well as bacteriological methods of warfare. Signed under the League of Nations, it entered into force in 1928 and represented an early global consensus that some weapons were simply beyond the pale.

However, the Protocol had serious weaknesses. It banned the use of chemical weapons but said nothing about developing, producing, or stockpiling them. In practice, many states treated it as a no-first-use agreement, reserving the right to retaliate in kind. It also did not clearly cover conflicts within a state’s own borders. As a result, nations continued to build chemical arsenals throughout the following decades, treating the treaty as a restriction rather than a true prohibition.

The Cold War stockpiles 🔗

Far from disappearing, chemical weapons grew more sophisticated and more numerous after the Second World War. During the Cold War, the United States and the Soviet Union built up enormous stockpiles of chemical weapons as part of their broader arms race. Scientists developed deadlier nerve agents, and new “binary” weapons emerged, in which two relatively harmless precursor chemicals are stored separately and combined only when the weapon is used.

This binary technology created a particular headache for arms control. Because the precursors themselves can appear harmless, they are far easier to store and conceal, complicating any future verification effort. By the 1980s, the Soviet Union alone was estimated to hold hundreds of thousands of tonnes of chemical agents. The world was now awash in weapons that the Geneva Protocol had failed to eliminate.

Iraq and the limits of the old rules 🔗

The clearest proof that the existing legal framework was failing came during the Iran-Iraq War of the 1980s. Iraq, which had ratified the Geneva Protocol back in 1931, used chemical weapons extensively against Iranian forces. Iraqi forces began with mustard gas and then, in March 1984, deployed the nerve agent tabun in what is considered the first use of a nerve agent in war.

The most notorious atrocity was directed at Iraq’s own people. On 16 March 1988, Iraqi aircraft attacked the Kurdish town of Halabja with a mixture of agents including mustard gas and the nerve agents tabun, sarin, and VX. Thousands of civilians, including women and children, were killed in a matter of hours. The United Nations Secretary-General had already formally accused Iraq of violating the 1925 Geneva Protocol in 1986, but international action was slow and weak. Halabja demonstrated that a ban on use alone, without verification or enforcement, was not enough.

The Chemical Weapons Convention: a stronger framework 🔗

The end of the Cold War created an opening for a far more ambitious treaty. The Chemical Weapons Convention (CWC) was opened for signature in 1993 and entered into force on 29 April 1997. Unlike the Geneva Protocol, the CWC aims to eliminate an entire category of weapons of mass destruction by prohibiting their development, production, acquisition, stockpiling, transfer, and use.

Crucially, the Convention requires every member state to destroy any chemical weapons and production facilities it holds. It is policed by the Organisation for the Prohibition of Chemical Weapons (OPCW), headquartered in The Hague. The OPCW’s inspectors monitor weapon destruction, verify former production sites, and routinely inspect industrial chemical facilities to ensure compliance. The organisation’s work was recognised with the 2013 Nobel Peace Prize. Today, 193 states are party to the Convention, making it one of the most widely adopted disarmament treaties in the world.

How the Convention is implemented at home 🔗

The CWC works only if each member state enforces it domestically. Every party must establish a National Authority to serve as the focal point for cooperation with the OPCW. This country signed the treaty in Paris in January 1993 as an original signatory and later enacted the Chemical Weapons Convention Act, 2000 to give the treaty domestic legal force. The National Authority Chemical Weapons Convention (NACWC), set up as an office of the Cabinet Secretariat, monitors compliance, regulates toxic chemicals and their precursors, and manages inspections of relevant chemical facilities. This combination of an international watchdog and a national authority is what gives the CWC real teeth.

Ongoing challenges in a treaty world 🔗

Despite the CWC’s success, the threat is not gone. A handful of states have remained outside the Convention, and the technical nature of chemical agents creates persistent problems. Because gases like chlorine dissipate quickly and must often be confirmed through autopsy, they offer attackers a degree of plausible deniability, making investigations slow and difficult.

Recent decades have shown how varied the danger has become. The 1995 sarin attack on the Tokyo subway by a cult demonstrated that non-state actors could produce and use nerve agents to cause mass panic. Syria’s government has been accused of using chemical weapons against its own civilians on multiple occasions, and the assassination of Kim Jong-nam with VX in 2017 showed these agents being used as tools of targeted killing. Dual-use chemistry, where the same factories that make pesticides or plastics could in theory make weapons, means that verification and vigilance can never truly stop.

What do you think? Given that ancient bans on poison failed for centuries and the Geneva Protocol failed to prevent stockpiling, what makes the verification system of the Chemical Weapons Convention more likely to succeed in the long run? And how should the international community respond when a state or non-state actor breaks the norm against chemical weapons use?

References

1. https://www.reachingcriticalwill.org/resources/fact-sheets/critical-issues/4582-chemical-weapons
2. https://www.history.com/articles/syria-chemical-weapons-history-facts
3. https://blogs.lse.ac.uk/lseih/2017/04/25/a-brief-history-of-chemical-warfare-from-sparta-to-syria/
4. https://stuyspec.com/article/the-history-of-chemical-warfare
5. https://time.com/4730885/history-chemical-weapons/
6. https://www.ebsco.com/research-starters/military-history-and-science/chemical-warfare
7. https://www.britannica.com/technology/chemical-weapon
8. https://disarmament.unoda.org/en/our-work/weapons-mass-destruction/secretary-generals-mechanism-investigation-alleged-use-chemical-and-biological-weapons-unsgm/1925-geneva-protocol
9. https://en.wikipedia.org/wiki/Geneva_Protocol
10. https://walterdorn.net/14-chemical-weapons-convention-overview
11. https://nuke.fas.org/guide/iraq/cw/program.htm
12. https://en.wikipedia.org/wiki/Halabja_massacre
13. https://en.wikipedia.org/wiki/Organisation_for_the_Prohibition_of_Chemical_Weapons
14. https://www.opcw.org/chemical-weapons-convention
15. https://www.pib.gov.in/PressReleasePage.aspx?PRID=2141792
16. https://chemicals.gov.in/organization-prohibition-chemical-weapons
17. https://nacwc.gov.in/