Weapons of Mass Destruction, or WMDs, are highly destructive weapons that cause a disproportionate amount of damage when compared to other weapons. Typically, these types of weapons are divided into three categories: nuclear, chemical, and biological. The first WMDs were the primitive chemical weapons developed during World War I. Nuclear weapons were introduced in the late 1940s after World War II. The Japanese were the first to develop deployable biological weapons during the 1930s and 1940s, but today all major nations have, or had, a major biological weapons program.