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.
South Vietnam in 1971. In accordance with the Paris Peace Accords signed with North Vietnam on 27 January 1973, US military forces withdrew from South Vietnam. North Vietnam was allowed to continue supplying communist troops in the South, but only to the extent of replacing materials that were consumed. The communist leaders had expected that the ceasefire terms would favour their side. But as Saigon began to roll back the Viet Cong, they found it necessary to adopt a new strategy, hammered out at a series of meetings in Hanoi in March 1973, according to the memoirs of Trần Văn Trà. As