United Nations: The United Nations played a central role in the Korean War. In response to North Korea's invasion of South Korea, the UN Security Council passed Resolution 82, which called for the immediate withdrawal of North Korean forces. The UN also established a Unified Command, led by the United States, to help South Korea repel the invasion. The Unified Command was composed of troops from various countries, including the United States, South Korea, and other UN member states.
Soviet Union: The Soviet Union supported North Korea throughout the war. It provided North Korea with military equipment, training, and advisers. Soviet pilots even flew combat missions in support of North Korea. However, the Soviet Union did not directly participate in the war on the ground.
China: China also supported North Korea during the war. It entered the war in October 1950, after the United Nations forces had crossed the 38th parallel and advanced into North Korea. Chinese troops helped to push the UN forces back to the 38th parallel and ultimately forced the United Nations to agree to a ceasefire.
United States: The United States played the leading role in the Korean War on behalf of the United Nations. It provided the bulk of the troops and equipment for the Unified Command and played a major role in the fighting. The United States also provided economic and political support to South Korea.
The Korean War ended in a stalemate in 1953 with the signing of the Korean Armistice Agreement. The agreement created a demilitarized zone (DMZ) between North and South Korea, which has remained in place to this day.