Before dawn on June 25, 1950, the Soviet-equipped North Korean People’s Army into the Republic of South Korea. Two days later, after an emergency session of the Security Council (which the Soviets voluntarily did not attend), the United Nations invited its members to help South Korea against the invasion. President Truman immediately involved US air and naval forces, and added ground troops a few days later.

The Korean War was the first ever "police action" to taken by the UN, however more importantly, it was a symbol of the Cold War: In a remote land, the forces of democracy (from US) would come up against the Communists (Soviet Union, with Communist China support). Despite the fact that there was never a formal declaration of war, the conflict escalated to a point where 20 nations were involved.

In the first weeks of war, the North Korean People’s Army steamrolled across South Korea, capturing the country’s port city, Inchon, and its capital, Seoul. They put pressure on the UN beachhead (an area in hostile territory that has been occupied and is held for further troops and supplies) at Pusan, on the southeastern tip of the Korean Peninsula.

Then General Douglas MacArthur, the 70-year-old World War II hero, was named supreme commander of UN forces. He executed a dramatic landing at Inchon, and recaptured Seoul in September. The United States launched a new goal: the unification of Korea. In October, UN troops invaded North Korea, took its capital, Pyongyang, and rolled on towards the Chinese border.

The move spurred on China to send in 180,000 of its own troops. A fresh Communist attack regained Pyongyang in December. By the end of the year, North Korea was again fully under Communist control. Then, on December 31, the Chinese, vowing to "liberate Korea" moved on Seoul. By January 15, they had recaptured it.