Vietnamese War, an undeclared war for the control of South Vietnam, 195775. The conflict began as a Communist guerrilla campaign supported by North Vietnam against the government of South Vietnam. By the mid-1960's, the fighting had expanded to full-scale warfare, with the United States becoming the major ally of South Vietnam. Several other anti-Communist nations, including South Korea, Australia. New Zealand, Thailand, and the Philippines, also aided South Vietnam.

The Vietnamese WarThe Vietnamese War saw major battles throughout the country.

The United States' participation was approved by four PresidentsEisenhower. Kennedy, Johnson, and Nixon. Each in turn acknowledged the necessity of supporting the South Vietnamese. The policy of the United States was initially expressed by Eisenhower in 1954. According to his "domino theory," if South Vietnam were toppled by the Communists, neighboring Asian nationsLaos, Cambodia, Thailand, Malaya, and Burmawould also fall, like a row of dominoes, to the Communists. The United States also feared at the time that if it withdrew from South Vietnam while that nation was still weak militarily, Communist nations would believe they could forcibly expand their sphere of influence unchecked.

The war ended with the North Vietnamese invasion and conquest of South Vietnam in 1975. A closely related development of that year was the fall of Laos and Cambodia to Communist movements in those countries.