Recovery of the Ssangseong Commandery

King Gongmin sent Yu In-u and others against the Ssangseong Commandery, recovering the land north of Cheollyeong after 99 years, with help from inside by Yi Ja-chun and his son Yi Seong-gye.

The commandery had been set up at Hwaju (Yeongheung) in 1258, when Jo Hwi and Tak Cheong killed the Goryeo officials and handed the region to the invading Mongols; it ruled the land north of Cheollyeong, and Jo Hwi’s descendants held the post of commander.

In 1356, right after purging Gi Cheol and other pro-Yuan figures, King Gongmin sent Yu In-u, military commissioner of the northeast, against Ssangseong. Yi Ja-chun, a local magnate who held a Yuan chiliarch’s post and was the father of Yi Seong-gye, sided with Goryeo and helped take the fortress from within, while the commander Jo So-saeng and others fled.

It was the signature achievement of Gongmin’s anti-Yuan reforms, and it launched the Yi family into Goryeo’s central politics. When Ming later announced it would set up a Cheollyeong Command to claim the region, Goryeo launched the Liaodong expedition, which ended in the Wihwado retreat (1388).