The Korean War was the 1950 to 1953 conflict between the Republic of Korea (South Korea) and the Democratic People’s Republic of Korea (North Korea). Because South Korea was aided by the United Nations and North Korea aided by China and the USSR, it became a localized proxy fight for the Cold War. Despite an armistice that ended the fighting, no formal peace treaty was ever signed.
From 1910 to 1945, Korea was occupied by Japan. Following World War II, the peninsula was divided between American and Soviet spheres at the 38th Parallel. On June 25, 1950, North Korean forces invaded the South. With the USSR boycotting the UN Security Council, President Harry Truman was able to secure UN support for the South.
Eventually, the United States provided almost 90 percent of the military assistance sent into South Korea. Rather quickly, UN forces, led by US Marines, repelled the North Koreans all the way to the Yalu River, North Korea’s border with China.
Chinese intervention pushed the UN forces back to the 38th Parallel, and much of the rest of the war was a stalemate characterized by static trench warfare. Negotiations led to the signing of an armistice on July 27, 1953. This agreement reestablished the border between the two Koreas at the 38th Parallel and created the Korean Demilitarized Zone (DMZ), the most heavily fortified border in the world.