Chemical Weapons


Chemical Weapons


Chemical weapons have been used since ancient times, for example poisoning drinking water in wells. Mustard gas, chlorine gas, and phosgene gas were used for the first time as a method of warfare on a large scale during the First World War by both the warring parties, resulting in approximately 91,000 dead and 1.2 million wounded. The first attack with chlorine gas was carried out by German forces in 1915, killing about 5,000 French soldiers. Germany also used mustard gas against British forces, who suffered more than 9,000 casualties. Later during the First World War, both France and Britain used chemical weapons against German soldiers. The horrors of chemical poison gases during the war provoked strong reactions in the public. Chemical weapons have since been regarded with abhorrence and have been condemned as particularly inhumane weapons, whose use is contrary to international humanitarian law.

Since it was already “forbidden to employ poison or poisoned weapons” in Article 23 of the Annex to Convention IV respecting the Laws and Customs of War on Land, which entered into force in 1910 and was ratified by all the warring parties, the use of chemical weapons in the First World War violated the customary international law codified by the Convention.

At the end of the war, Article 171 of the Treaty of Versailles of 1919 (the Treaty of Peace between the allied and associated powers and Germany) prohibited “the use of asphyxiating, poisonous or other gases and all analogous liquids, materials or devices being prohibited, their manufacture and importation are strictly forbidden in Germany.”

During the years between the two world wars, chemical weapons were used in Abyssinia (now Ethiopia) by Italy in 1935–36 and by Japan against China between 1937 and 1945. During the Second World War, poison gas (Zyklon B or hydrogen cyanide) was used to murder millions of people – mainly Jews – in gas chambers in German extermination camps (e.g., Auschwitz-Birkenau, Treblinka, and Sobibór), but not on the battlefields of Europe – probably because of fear of retaliation. Chemical weapons continued to be produced on a large scale during the Second World War in a number of countries. During the Cold War, large quantities of chemical weapons were developed, produced, and stored – especially in the United States and the Soviet Union. During the 1970s and 1980s, about twenty-five other countries developed the capabilities to produce chemical weapons.

Chemical weapons were used by Egypt in Yemen from 1963 to 1967 and by Iraq during the war against Iran from 1980 to 1988. Both countries are parties to the 1925 Protocol prohibiting the use of poisonous gases. In 1988, the Iraqi government used chemical weapons (sarin and mustard gas) against its own Kurdish population in the town of Halabja in the northern part of Iraq. An estimated 5,000 to 8,000 people were killed by the poison gas attack. Sarin nerve gas was used by the Japanese sect Aum Shinrikyo against civilians in 1994, in the city of Matsumoto, and in 1995 in Tokyo’s subway, killing thirteen people. In the late 1990s, Al-Qaeda had a development program for producing chemical weapons in the eastern part of Afghanistan. In the ongoing civil war in Syria, government forces have used poison gas (sarin nerve gas) several times against the civilian population, in December 2012 and in March and August 2013. According to US intelligence sources, 1,429 people, including 426 children, were killed by the poison gas attack in August 2013. During the Vietnam War, the United States used chemicals (toxic Dioxin) as defoliants and to destroy agricultural crops. Between 1962 and 1971, the US military sprayed nearly 20 million US gallons (75.7 million litres) of chemical herbicides and defoliants – called “Agent Orange” – in Vietnam, Eastern Laos, and parts of Cambodia, as part of the aerial defoliation program known as “Operation Ranch Hand.” More than 20 per cent of South Vietnam’s forests were sprayed at least once over the nine-year period. Millions of Vietnamese citizens – the government of Vietnam claims that the number is around 4 million – were exposed to Agent Orange. The majority of the victims – an estimated 3 million people – suffered illnesses because of it, including serious skin diseases, a variety of cancers, and deformed babies. The above figures include the children of people who were exposed. Many US veterans suffer increased rates of cancer, and nerve, digestive, skin, and respiratory disorders. At the time of the Vietnam War, there were no specific provisions on herbicidal warfare in international humanitarian law or customary law. In 1976, a draft convention on the subject, which had been prepared in a working group under the Conference of the Committee on Disarmament, was presented to the United Nations General Assembly. In 1976, the Assembly, by resolution 31/72, adopted the Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques (the Environmental Modification Convention or ENMOD Convention). The resolution was adopted with 96 votes in favour, including the United States, 8 against, and 30 abstentions. The Convention was opened for signature and ratification in 1977 and entered into force in 1978. The Convention prohibits the military or other hostile use of environmental modification techniques that have widespread, long-lasting, or severe effects. Many states do not regard this as a complete ban on the use of herbicides and defoliants in warfare as the Convention requires a case-by-case consideration.


The prohibition of chemical weapons (poison gases) goes back to 1925, when the Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare was adopted (see chapter 6 on biological weapons).


Negotiations on a comprehensive ban on chemical weapons began in 1980 at the UN Disarmament Conference and the draft convention was adopted by the Conference in 1992. In November 1992, the United Nations General Assembly adopted a resolution that recommended concluding a convention on the prohibition of chemical weapons on the basis of the negotiated draft convention. The resolution (47/39) was adopted without a vote.

The CWC was signed in 1993 by 130 countries. As of January 2016, the Convention had been ratified or adhered to by 192 countries. Israel has signed the CWC, but has not yet ratified it. Three countries have neither signed nor adhered to the CWC: Egypt, North Korea, and South Sudan. The 192 countries represent 98 per cent of the world’s population and also 98 per cent of the global chemical industry. The CWC entered into force in 1997.

Syria joined the CWC in September 2013 and issued a declaration promising to comply with the provisions, and to apply the Convention provisionally pending the formal entry into force for Syria (30 days after the agreement). Two days after the CWC entered into force for Syria, the first inspectors from the Organization for the Prohibition of Chemical Weapons arrived in the country. The Syrian production plants for the manufacture of chemical weapons were destroyed by 1 November. After some diplomatic wrangling and protracted negotiations between the United States and Syria’s closest ally, Russia, the UN