Vietnam War
the Vietnam War happened between 1959-1975. North Vietnam was a communist country and South Korea was not. The United States supported South Vietnam and they eventually entered the war. America had a hard time with combat because of the harsh conditions of the jungles that they weren't used to. They eventually backed out when Richard Nixon became president in 1969, so it was considered a loss for the United States. On January 27, 1973 a peace fire was eventually agreed and the war ended in 1975.
http://www.ducksters.com/history/cold_war/vietnam_war.php