Nerve agent
Geneva Protocol of 1925: This agreement was signed on June 17, 1925, and took effect on February 8, 1928.  It permanently bans the use of all forms of chemical and biological warfare. The agreement was signed after World War I, where mustard gas and other chemical weapons were used.  People were afraid that chemical and biological warfare could have terrible effects in any future war. The protocol was extended by the Biological Weapons Convention (1972) and the Chemical Weapons Convention (1993).