President Richard Nixon signs a ban on the development, production and stockpiling of biological and toxin weapons known as the Biological and Toxin Weapons Convention. The pact is signed on April 10, 1972, simultaneously by leaders in Washington, London and Moscow. It is ratified on March 26, 1975. To date, more than 160 nations have signed the agreement, which bans offensive and defensive uses of such weapons. Three years before the agreement, the United States had halted its production of biological weapons.