History of Vietnam since 1945 unstable as no government could keep power for long. There were more coups, often more than one every year. The Communist-run Viet Cong expanded their operation and scored some significant military victories during this period. In 1965, US President Lyndon Johnson sent troops to South Vietnam to secure the country and started to bomb North Vietnam, assuming that if South Vietnam fell to the Communists, other countries in the Southeast Asia would follow, in accordance with the domino theory. Other US allies, such as Australia, New Zealand, South Korea, Thailand, the Philippines, and Taiwan also sent troops to South Vietnam.
Cannabis in Vietnam in areas controlled by the Hòa Hảo sect, for fear of driving them to join the National Liberation Front. In the 1960s, the United States government became concerned with cannabis use by US troops in the Vietnam War. Though alcohol was the drug most commonly used by American troops in the Vietnam War, cannabis was the second-most common. Initially rates of usage among deployed soldiers were comparable to those of their stateside peers, with 29% of troops departing Vietnam in 1967 reporting having ever used marijuana in their lives. A 1976 study however showed that from 1967–1971, the proportion of