The history and properties of chemical weapons
Chemical weapons are chemicals formulated to inflict harm on humans. Modern chemical weapons are usually delivered by means of missiles, shells, or gravity bombs. By their very nature, chemical weapons are highly indiscriminate and cause superfluous injury. Due to their capacity to cause death and suffering on a wide scale, they are commonly labelled ‘weapons of mass destruction’.
The Second Battle of Ypres in 1915 witnessed history’s first ‘successful’ large-scale use of chemical weapons, as German troops released over 150 tons of chlorine gas – dispersed by wind – along the Allied front. Around 5000 French–Algerian troops were killed almost instantly. After Ypres, chemical weapons – mainly chlorine and mustard agents – were used as force multipliers in many battles. More than 90.000 deaths (and numerous people suffering permanent nerve damages) are attributable to the introduction of gas agents to the battlefields of the First World War. The gas attacks left soldiers temporary blind and caused horrific scenes, some of which were powerfully recorded by war poets like Wilfred Owen.
Motivated by putting an end to the indiscriminate effects and superfluous injury caused by chemical weapons, the use of such weapons in armed conflict was banned under the 1925 Geneva Protocol. While this ban was a crucial step in stigmatising chemical weapons, loopholes remained. Crucially, the Protocol did not prohibit possession and manufacture of chemical weapons, and some States Parties reserved the right to use chemicals weapons against non-parties or in reprisal. Nevertheless, since the adoption of the Geneva Protocol, the use of chemical weapons has been viewed as both morally and legally unacceptable.
Chemical weapons were generally not used in hostilities during the Second World War, but poison gas was heavily relied upon to carry out the Holocaust and several atrocities against prisoners of war in the Asia–Pacific theatre. The Iran–Iraq war in the 1980s, however, saw widespread use of chemical weapons, as Saddam Hussein’s Iraqi forces used sarin and mustard agents against both Iranian and Kurdish forces and civilians. On 16 March 1988, between 3000 and 5000 people, most of whom were Kurdish civilians, were killed in the ‘Halabja Massacre’ in the final stages of the Iran–Iraq War. The number of long-term casualties of the attack was probably also in the thousands.
To fill the gaps left by the Geneva Protocol, the Conference on Disarmament (CD) adopted the Chemical Weapons Convention (CWC) on 3 September 1992, after twelve years of negotiations. The Convention, which bans the use, production and stockpiling of chemical weapons, entered into force on 29 April 1997. The Organisation for the Prohibition of Chemical Weapons (OPCW) was established to facilitate universalization and implementation of the Convention, which now has 190 States Parties. Israel and Myanmar have signed but not ratified the Convention. Angola, Egypt, North Korea, and South Sudan have neither signed nor acceded to it.
Since the adoption of the CWC, few instances of chemical weapons use have occurred. After it was disclosed that regime forces had used chemical weapons in the Syrian Civil War in 2013, Syria was compelled to accede to the Convention. Nevertheless, use of chemical weapons has continued in the Syrian Civil War, mainly through attacks by the so-called Islamic State. Chemical weapons have also allegedly been used by non-state armed groups in Afghanistan and Nigeria, and was utilised in a spectacular terrorist attack on the Tokyo subway in 1995.
 Chemical weapons were, however, used by Japanese forces during the invasion of Manchuria in 1937.