The late Vietnam War and US defeat
From 1965 to 1968, large numbers of US troops in Vietnam encountered fierce opposition from the North Vietnamese and attacks from Viet Cong troops.
Meanwhile, back home, large-scale protests against the Vietnam War were organized. The opposition became stronger once Americans learned about brutal killings committed by American soldiers, such as the Mai Lai massacre of March 1968.
Richard Nixon became President in 1969 and supported the retreat of US troops from Vietnam by giving financial aid to the South Vietnamese Army, instead. In 1969, a series of demonstrations were held across the US, calling for an end to the Vietnam War. However, the US troops still got involved in conflicts, attacking Cambodia (1970) and Laos (1971) in their pursuit of the Viet Cong.
A cease-fire agreement was reached in January 1973, and by March, the last American troops returned from South Vietnam. Two years later, the war ended when Saigon, the capital of South Vietnam, was taken over by the communists from the North.
In general, the Vietnam War is seen as a failure for the US because it did not prevent communists from taking over Vietnam. The US had gotten involved in the war expecting a quick victory. However, losing the war exposed the faults in the US’s approach to communist containment, which relied heavily on a competition with the Soviet Union over who had the most influence in other countries. After the Vietnam War, the US began to transform its policy of containment, focusing more on developing diplomatic relations with the Soviet Union.