The Vietnam War
The Vietnam War which lasted from 1955-1975, followed the First Indochina War, or the French Indochina War. Vietnam was French Indochina, a French colony, until 1954.
Within the country there was a movement called the Vietminh led by Ho Chi Minh, who wanted foreign groups, the French and Japanese (who invaded in the Second World War), to leave. At the time, the United States supported them because they were at war with Japan.
However, France did not want to leave, and after Ho Chi Minh declared the Vietnamese Declaration of Independence, they bombed Vietnam to allow them to stay. This continued from 1946-1954 in the First Indochina War. While Truman and the United States wanted to support independence, they could not now because Ho Chi Minh and communism were their enemy (though he actually favoured nationalism before communism), and they did not want to anger their NATO ally France.
In 1954 France left the War after losing Dien Bien Phu and at the Geneva Accord the same year France, Britain, the United States (though neither they or South Vietnam signed), the Soviet Union, and China, came to the conclusion that Vietnam would be partitioned at the 17th parallel, giving Laos and Cambodia their freedom. This would last until 1956 when there would be an election and then it would be reunited. Thus all the Vietminh could go into the North and those who were against communism to the South.
Things did not end up that way though, as North and South Vietnam did not cooperate for elections. The country did not become one until 1975 when the communists took over the whole country.
The South was led by Ngo Dinh Diem, a Catholic who favoured other Catholics and his system was rather corrupt, relying on military control. The military, ARVN (The Army of the Republic of Vietnam) did not do well even though they were supported by the United States.
Meanwhile, the communists in the North were actually quite popular, leading to a movement in the South which Ho Chi Minh supported. By the end of the decade this insurgency who called themselves the National Liberation Front (NLF), wanted to get rid of Diem. The United States became nervous and under John F. Kennedy, Diem was removed, and ended up being killed in 1963.
The United States was given support for war by congress after an American ship was attacked, supposedly by North Vietnam, in the Gulf of Tonkin. This led to American soldiers being sent in to support ARVN and Operation Rolling Thunder, the bombing of the North for supporting the NLF from February 1965 to March 1968. Bombing was failing but American soldiers were increased to about 500 000 by 1968.
In 1969 North Vietnam undertook the Tet Offensive, which made it all the way to the American embassy in Saigon. Though they were pushed back, support waned. This led to putting the emphasis back onto South Vietnam’s involvement instead of America’s. Secret negotiations were undertaken from 1968-1973 culminating in the Paris Peace Accords in January of 1973, calling for a peaceful unification. However, North Vietnam invaded South Vietnam in 1975 against it, and the country became communist.