 MacArthur's amphibious landings at Incheon had severed the North Korean Army's supply lines; as a result, North Korea's army had begun a lengthy retreat from South Korea into North Korea.This retreat was closely monitored by the People's Republic of China (PRC), out of fear that the UN offensive against Korea would create a US-backed enemy on China's border, and out of concern that the UN offensive in Korea could evolve into a UN war against China.The latter of these two threats had already manifested itself during the Korea War