I. Korean War (1950 – 1953)
During the Cold War between the Soviet Union and the United States, Korea was split into two regions, with separate governments. Since both governments claimed to be the "real" government of all of Korea, a conflict eventually escalated into open warfare on June 25, 1950. After the North Korean invasion, the United Nations Security Council called for an immediate ceasefire. Twenty-one countries from the United Nations contributed to the UN force, with the United States providing 88% of the UN's military personnel.
The fighting ended on July 27, 1953, when an armistice was signed. The agreement created the Korean Demilitarized Zone to separate North and South Korea. Since no peace treaty has been signed, the two Koreas are still at war until this day.