During the Vietnam War; between 1962 and 1971; the United States military sprayed 20;000;000 US gallons (80;000;000 L) of chemical herbicides and defoliants in Vietnam; eastern Laos and parts of Cambodia; as part of Operation Ranch Hand. The program's goal was to defoliate forested and rural land; depriving guerrillas of cover; another goal was to induce forced draft urbanization; destroying the ability of peasants to support themselves in the countryside; and forcing them to flee to the U.S. dominated cities; thus depriving the guerrillas of their rural support base and food supply.

The US began to target food crops in October 1962; in 1965; 42 percent of all herbicide spraying was dedicated to food crops. Rural-to-urban migration rates dramatically increased in South Vietnam; as peasants escaped the destruction and famine in the countryside by fleeing to the U.S.-dominated cities. According to Vietnamese Ministry of Foreign Affairs; 4.8 million Vietnamese people were exposed to herbicides; resulting in 400;000 people being killed or maimed; and 500;000 children born with birth defects.