In the mid-14th century, when the Yuan dynasty was beginning to crumble due to the Red Turban Rebellion, Gongmin reformed the Korean government, abolished Mongolian military outposts, purged pro-Yuan sentiments, and regained lost northern territories.
The Red Turban army led by Mao Ju-jing invaded Goryeo and took the city of Pyongyang.
In January 1360, the Goryeo army led by An U and Yi Bang-sil retook Pyongyang and the northern region which had been captured by the Red Turbans.
Of the Red Turban army that had crossed the Yalu River, only 300 troops returned to Liaoning after the war.
In 1388, unwilling to lead the invasion of Liaodong and fight the Ming dynasty, General Yi Sŏng-gye decided to revolt against U of Goryeo and his fellow general, Ch'oe Yŏng, and swept back to the capital, Gaegyeong, to secure control of the government.