Which objective of american foreign policy in 1951 led to a united nations military intervention in the korean peninsula?

During the 1950's, the US had adopted a policy of containment. The goal was to stop the spread of communism on a global scale. This included giving financial and military aid to countries who might fall into the hands of a communist government. A perfect example of this would be South Korea.

During the early 1950's, North Korea (a communist country) invaded South Korea. America, worried about the spread of communism, wanted to ensure that South Korea stayed free of this communist system. To do this, the US helped convince the United Nations to intervene in the conflict between North and South Korea.