The Vietnam War ended with Vietnam being united as a single, communist country.
The Korean War ended with North Korea (communist) and South Korea (non-communist) remaining separate countries.
The United States did not accomplish its intended mission in Vietnam, which was to prevent the spread of communism in that country. After many years and many lost lives, the US pulled out of that effort in 1973. South Vietnam fell to the communist forces of North Vietnam in 1975, and a unified Vietnam (under communist rule) was established in 1976.
In Korea, when communist forces from the North invaded the South in 1950, the United States intervened (with United Nations backing), battled to keep South Korea free and democratic, and were able to do so.