Third Battle of Seoul - Wikipedia

4 JAN 1951 - UN forces abandon Seoul, Korea, to the Chinese Communist Army.

The Third Battle of Seoul was a battle of the Korean War, which took place from December 31, 1950, to January 7, 1951, around the South Korean capital of Seoul. It is also known as the Chinese New Year's Offensive, the January–Fourth Retreat (Korean: 1·4 후퇴) or the Third Phase Campaign Western Sector[nb 4] (Chinese: 第三次战役西线; pinyin: Dì Sān Cì Zhàn Yì Xī Xiàn).

In the aftermath of the major Chinese People's Volunteer Army (PVA) victory at the Battle of the Ch'ongch'on River, the United Nations Command (UN) started to contemplate the possibility of evacuation from the Korean Peninsula. Chinese Communist Party chairman Mao Zedong ordered the Chinese People's Volunteer Army to cross the 38th Parallel in an effort to pressure the UN forces to withdraw from South Korea.