I think you have it very wrong: "After the first two months of war, South Korean Army (ROKA) and the US forces rapidly dispatched to Korea were on the point of

I think you have it very wrong: "After the first two months of war, South Korean Army (ROKA) and the US forces rapidly dispatched to Korea were on the point of defeat. As a result, the ROKA and US troops retreated to a small area behind a defensive line known as the Pusan Perimeter. In September 1950, an amphibious UN counter-offensive was launched at Incheon, and cut off many KPA troops in South Korea. Those who escaped envelopment and capture were forced back north. UN forces invaded North Korea in October 1950 and moved rapidly towards the Yalu River—the border with China—but on 19 October 1950, Chinese forces of the People's Volunteer Army (PVA) crossed the Yalu and entered the war.[51] The surprise Chinese intervention triggered a retreat of UN forces back below the 38th Parallel by late December." I can't find anything related to US/UN forces invading. But this is most likely a western view of the war. China looks like anything but just standing idly by during the war (did not realize that China was deeply involved in the Korean War before).