 In the wake of the United Nations (UN) forces'successful landing at Inchon and the subsequent destruction of the Korean People's Army (KPA) by mid-1950, the Eighth United States Army crossed the 38th parallel and advanced rapidly towards the Sino-Korean border. Alarmed by this development, China's Chairman Mao Zedong ordered the Chinese People's Volunteer Army (PVA) to intervene in Korea and to launch the First Phase Campaign against the UN forces. Between October 25 and November 4, 1950, the PVA 13th Army surprised and defeated the Republic of Korea (ROK) II Corps and the US 1st Cavalry Division in a series of battles around Onjong and Unsan, destroying the right flank of the US Eighth Army while forcing the UN forces to retreat back to the Ch 'ongch'on River. Although Chinese forces were able to break through the UN line, logistics difficulties forced the Chinese to withdraw on November 5, 1950.
