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.
Air transport in Vietnam and commercialization of air transportation. The aviation sector expanded greatly during its formative years, expanding from a few aircraft in what was then North Vietnam to eventually include a fleet of over 50 aircraft (including both Soviet- and US-made) in a unified Vietnam after 1976. Infrastructure was improved during this time, as airports country-wide were equipped with better facilities and materials for flight management and operations. CAAV grew to serve around 250,000 passengers a year, both domestically and on international routes to China, Laos, Cambodia and Thailand. On 9 December 2004, United Airlines made history when its Boeing 747-400 landed