History of chemical warfare

The history of chemical warfare dates from antiquity. Chemical weapons have been a part of warfare in most societies for centuries. However, their usage has been extremely controversial since the 20th century.

Chemical warfare is recorded in the ancient periods of Greece, Rome, Carthage, India, China, and South Africa. Soldiers poisoned arrows, water supplies, or dispersed toxic smokes.

Chemical weapons were first used on a large scale by most major powers in World War I, employing the gases mustard, phosgene, and chlorine, and others, causing lung scarring, blindness, and death. During World War II, Nazi Germany used a commercial hydrogen cyanide blood agent named Zyklon B to commit industrialised genocide against Jews and other populations in gas chambers. The Holocaust resulted in the largest death toll to chemical weapons in history. The Empire of Japan also used chemical warfare in China during the Second Sino-Japanese War, including mustard gas and lewisite.

Nazi Germany discovered nerve agents during the war, but did not use them for fear of Allied retaliation. In the Cold War, many countries stockpiled chemical weapons. The Soviet and United States chemical weapons programs became the first and second largest in world history, focusing on sarin, VX/VR, and mustard, primarily for battlefield use in Europe. The use of chemical weapons in the Iran–Iraq War and in the Syrian civil war saw thousands killed by nerve agents and blister agents.

At the end of the Cold War, the 1993 Chemical Weapons Convention sought a legally binding, worldwide ban on the production, stockpiling, and use of chemical weapons and their precursors. Large-scale stockpile destruction efforts followed, with the US eliminating its arsenal by 2023. As of 2025 the treaty has 193 state parties; Syria and Russia are widely believed to have violated its prohibitions on stockpiling and use while Israel and North Korea remain non-parties. Small research quantities are treaty-permitted as part of CBRN defense.