The term chemical warfare agent was a 20th century military name used to describe a chemical compound that could be used to injure or kill opposing forces on the battlefield. However, the history and use of chemical warfare agents started long before the 20th century.2 From ancient times to the 19th century, humans identified and used naturally occurring poisons, toxins, diseases, noxious fumes, incapacitants, and incendiaries to achieve military victory over an opponent. Drawing on the knowledge of the past, during World War I, the participants developed, produced, and used large amounts of chemical warfare agents on the battlefield. During the 1920s and 1930s, several countries continued to use chemical warfare agents in various conflicts around the world. The list of potential chemical warfare agents grew during World War II and afterward as advances in chemistry created new, deadlier agents. Following World War II, some countries used chemical warfare agents against both their enemies and their own people. This led terrorist organizations to take note of what became known as weapons of mass destruction and launch attacks against cities and individuals, no longer limiting chemical warfare agent production to governments and use to the battlefield. Despite several treaties to ban their use and the general abhorrence of them, chemical warfare agent attacks continued into the 21st century.