25 October 1950
Chinese Troops Enter North Korea
The United Nations advance across North Korea continued through the month of October, despite repeated warnings from Mao Zedong that the People’s Republic of China would not tolerate the presence of non-Korean troops north of the 38th parallel. MacArthur assured Truman that this was no more than a bluff, but to remain on the safe side the administration ordered MacArthur that only South Korean forces should enter the three provinces along the Yalu River—which formed the border between North Korea and China.

In spite of this precaution, 300,000 Chinese troops came pouring across the Yalu River on October 25. At this point the tide of war changed again, with United Nations forces in full retreat. U.S. forces suffered heavy losses in the battle of the Chosin Revervoir in early December, and near the end of that month some 100,000 UN troops, along with 100,000 South Korean civilians, were evacuated from the port city of Hungnam. Seoul fell once again to the communists in January 1951, and MacArthur began to call for the use of atomic weapons to stop the Chinese advance.

- United Nations Advance to the Yalu River

- Chinese Communist Offensive in North Korea

- The Chinese Offensive, 25 November 1950 - 25 January 1951

- The War Stabilizes, 25 January - 30 June 1951