During the first several months of the Korean War, from June to September 1950, the North Korean Korean People's Army (KPA) succeeded in occupying most of the Korean Peninsula, rapidly routing U.S. and South Korean forces. On 15 September 1950, UN forces reversed the situation by landing behind North Korean lines at Incheon and forcing the KPA to retreat to the north. The situation reversed again when Chinese troops entered the conflict on 19 October, triggering a retreat by UN troops until early 1951.