The Korean War (25 June 1950 – armistice signed 27 July 1953) was a conventional war between South Korea, which was supported by the United Nations, and North Korea, which was supported by the People's Republic of China (PRC) and had military material (and fighter pilots) provided by the Soviet Union. The war was a result of the physical division of Korea by an agreement of the victorious Allies at the conclusion of the Pacific War, at the end of World War II.
The Korean peninsula was ruled by Japan from 1910 until the end of World War II. Following the surrender of Japan in 1945, American administrators divided the peninsula along the 38th Parallel, with United States troops occupying the southern part and Soviet troops occupying the northern part.
The failure to hold free elections throughout the Korean Peninsula in 1948 deepened the division between the two sides, and the North established a Communist government. The 38th Parallel increasingly became a political border between the two Koreas. Although reunification negotiations continued in the months preceding the war, tension intensified. Cross-border skirmishes and raids at the 38th Parallel persisted. The situation escalated into open warfare when North Korean forces invaded South Korea on 25 June 1950. The Korean War was the first significant armed conflict of the Cold War.
The United Nations, led by the United States, came to the aid of South Korea in repelling the invasion, but within two months the defenders were pushed back to the Pusan perimeter, a small area in the south of the country, before the North Koreans were stopped. A rapid UN counter-offensive then drove the North Koreans past the 38th Parallel and almost to the Yalu River, at which time the People's Republic of China (PRC) entered the war on the side of the North.
The Chinese launched a counter-offensive that pushed the United Nations forces back across the 38th Parallel. The Soviet Union provided material aid to the North Korean and Chinese armies. In 1953, the war ceased with an armistice that restored the border between the Koreas near the 38th Parallel and created the Korean Demilitarized Zone (DMZ), a 2.5 mile (4.0 km) wide buffer zone between the two Koreas. Minor outbreaks of fighting continue to the present day.
Both North and South Korea were sponsored by external powers. From a military science perspective, the war combined strategies and tactics of World War I and World War II: it began with a mobile campaign of swift infantry attacks followed by air bombing raids, but became a static trench war by July 1951.
