After World War II, Korea was divided along the 38th parallel, with the Soviet Union occupying the northern half and the United States occupying the southern half. In 1950, North Korea invaded South Korea, and the United States intervened to support South Korea. The Korean War lasted for three years and ended in a stalemate, with the two Koreas still divided today.
The United States had several reasons for intervening in the Korean War. First, the United States was concerned about the spread of communism in Asia. The United States believed that if North Korea were allowed to conquer South Korea, other communist countries in Asia might be emboldened to invade their neighbors. Second, the United States wanted to prevent the Soviet Union from gaining control of Korea. The United States believed that if the Soviet Union controlled Korea, it would have a significant advantage in the Cold War. Third, the United States wanted to support South Korea's right to self-defense. The United States believed that South Korea had the right to defend itself against North Korean aggression.
Vietnam War
After the French withdrew from Vietnam in 1954, the country was divided into two parts, North Vietnam and South Vietnam. North Vietnam was communist, while South Vietnam was pro-Western. The Vietnam War began in the 1950s, when North Vietnam launched a campaign to unify Vietnam under communist rule. The United States intervened in the Vietnam War in 1965, and the war lasted until 1975. The Vietnam War ended in a communist victory, and Vietnam is now a socialist state.
The United States had several reasons for intervening in the Vietnam War. First, the United States was concerned about the spread of communism in Southeast Asia. The United States believed that if Vietnam fell to communism, other countries in Southeast Asia might be next. Second, the United States wanted to support South Vietnam's right to self-defense. The United States believed that South Vietnam had the right to defend itself against North Vietnamese aggression. Third, the United States was concerned about losing its reputation as a world power. The United States believed that if it did not intervene in Vietnam, it would appear weak and unable to defend its allies.