Answer:
The United States was successful in containing communism in South Korea, since it prevented its expansion into South Korea through its participation in the Korean War.
Explanation:
The Korean War was fought between 1950 and 1953 between communist North Korea and prowest South Korea. North Korea was militarily supported in the war by the People's Republic of China and the Soviet Union. South Korea was supported by the United Nations and received military assistance from various UN countries, led by the United States.
The direct cause of the conflict was the division of the Korean territory, that was annexed by Japan in 1910 after World War II. The northern part was occupied by the Soviet Union and the southern part by the United States. The 38th parallel was taken as the dividing line. The division would be temporary, but both parts soon developed into their own entities. The northern part became communist and the south became democratic. There was soon no longer a question of a peaceful merger of the two parts, and both parts considered using military force to conquer the other part.
After various border conflicts, the war started on June 25, 1950 with an invasion of North Korea on the south and ended on July 27, 1953 with a ceasefire, without a real winner having emerged. The new dividing line came close to the 38th parallel.
The most important result of this war was the rejection of communism from South Korea, which constituted itself as a main democratic force in Asia, along with Japan, thanks to the American support in the conflict.