Defoliation, a form of chemical warfare, is the use of herbicides to destroy plant or forest landcover in order to improve visibility and cut off food supplies to the enemy. The use of chemical herbicides cannot be limited to affecting only the enemy, however. It both drifts over borders into neutral neighbouring areas and countries and also affects innocent civilians and animals in the warring countries themselves. Chemical agents have been proved to produce birth defects in humans and animals; have caused the starvation of civilians due to the destruction of food crops (sometimes so completely as to render regeneration impossible); have caused the death - and possible extinction - of species of animals which depend on foliage for food and concealment; and leave toxic residual in humans and animals which can eventually accumulate to lethal levels.
The first chemical to be used in warfare was chlorine gas in World War I, although during the course of the war other chemicals were used as well. Italy used chemical weapons against Ethiopia in 1935-1936 and both Ally and Axis powers produced and stockpiled chemical weapons in World War II. The Geneva Protocol (1925) and the Bacteriological and Toxin Convention (1972), the key documents prohibiting biochemical warfare, have not been successful in preventing its use. The first document outlawed first-use but failed to prohibit either possession or retaliatory use; the second bans the production, possession, transfer, and use of chemical weapons but lacks verification procedures. It has been more the fear of retaliation (thus leading to usage mainly against those countries unable to reciprocate) than legal or moral restrictions that have limited usage. The Chemicals Weapons Convention, which was opened for signature in 1993 and is expected to come into force in 1995, specifically mentions herbicides in the preamble: that the State parties recognize "the prohibition, embodied in the pertinent agreements and relevant principle of international law, of the use of herbicides as a method of warfare".
In the Vietnam War, the USA used considerable amounts of herbicides against Vietnam; in 1967, 50 million lbs of herbicides were sprayed over 1 million acres of South Vietnam; in 1968 10 million gallons infected 4 million acres (one third of which was crop land); usage was discontinued in 1970. A 1971 report shows that by 1970, 1.2 million acres of mangrove forests in Vietnam had been totally destroyed and 600,000 people had been cut off from their food supplies. Records from a Saigon children's hospital indicate a dramatic increase (from 26 per 1000 to 64 per 1000) in cleft palate, spina bifida, and other birth defects after 1966, the year in which heavy antiplant spraying began. In 1984, Kampuchea complained to the United Nations Commission on Human Rights that the Vietnamese occupying forces in Kampuchea were using chemical weapons in water sources and food supplies, leading to severe diarrhoea, dysentery, fever, and possible death.