The nations involved in the Vietnam War included; The Republic of Vietnam, the United States, Australia, New Zealand, South Korea, the Philippines and Thailand. These countries fought against: The Democratic Republic of Vietnam (North Vietnam), the People's Liberation Armed Forces in South Vietnam (Viet Cong), the Khmer Rouge (communist guerrillas in Cambodia) and the Pathet Lao (communist guerrillas in Laos). The ones that we generally focus on are Vietnam, Laos, and Cambodia.
Inspired by Chinese and Soviet communism, Ho Chi Minh formed the Viet Minh, or the League for the Independence of Vietnam, to fight both Japan and the French colonial administration. Japan withdrew its forces in 1945, leaving the French-educated Emperor Bao Dai in control of an independent Vietnam. Ho’s Viet Minh forces rose up immediately, seizing the northern city of Hanoi and declaring a Democratic Republic of Vietnam (DRV) with Ho as president. Seeking to regain control of the region, France backed Bao and set up the state of Vietnam (South Vietnam) in July 1949, with Saigon as its capital. Armed conflict continued until a decisive battle at Dien Bien Phu in May 1954 ended in French defeat by Viet Minh forces.
When things started to go badly in Vietnam, nearby Cambodia and Laos became targets.
The U.S. government enlarged the Vietnam War into Laos for two principal reasons: to put down the Pathet Lao insurgency, which was waging an intensifying war against a U.S.-installed, right-wing dictatorship in Laos; and to stop the flow of goods on the so-called Ho Chi Minh trail, used to bring supplies from north Vietnam to the south, passing partly through Laos.
The U.S. government enlarged the Vietnam War into Laos for two principal reasons: to put down the Pathet Lao insurgency, which was waging an intensifying war against a U.S.-installed, right-wing dictatorship in Laos; and to stop the flow of goods on the so-called Ho Chi Minh trail, used to bring supplies from north Vietnam to the south, passing partly through Laos.
The U.S. government viewed American involvement in the war as a way to prevent a Communist takeover of South Vietnam. This was part of a wider containment strategy, with the stated aim of stopping the spread of communism. According to the U.S. domino theory, if one state went Communist, other states in the region would follow, and U.S. policy thus held that accommodation to the spread of Communist rule across all of Vietnam was unacceptable.