Political map of East Asia and the Western Pacific 9 September 1951 (China in Korea and Tibet): China's intervention in Korea (People's Volunteer Army) forced the surprised UN forces to retreat, but the Chinese were unable to conquer the South and a stalemate ensued. Meanwhile, the People's Republic was moving to reassert Chinese authority over Tibet. In a short campaign over the disputed Chamdo region (Battle of Chamdo), it forced Tibet to sue for peace and accept Chinese sovereignty (Seventeen Point Agreement for the Peaceful Liberation of Tibet).