Battle of Gwiju: Goryeo routs the Khitan army

Goryeo had faced Khitan pressure since the first Liao invasion of 993, after which the diplomat Seo Hui secured the lands up to the Yalu River. In 1009 the general Gang Jo deposed and killed King Mokjong; at the end of 1010 Emperor Shengzong of Liao invaded with, by the Korean count, 400,000 men, and early in 1011 he defeated and executed Gang Jo and burned the capital, Gaegyeong, while King Hyeonjong, on Kang Gam-chan's advice, fled south to Naju. The Liao withdrew but demanded six fortresses on the lower Yalu and that the king come to court in person; Goryeo refused, and raids followed in 1015–1017. In 1011, in the middle of the war, the court began carving the woodblocks of the first Korean Buddhist canon, hoping for the Buddha's protection; the work was completed only in 1087.

In January 1019 the Liao commander Xiao Paiya — whom the Korean chronicle calls Xiao Xunning — crossed the Yalu with an army said to number 100,000. Kang Gam-chan, then over seventy, was made commander-in-chief with Kang Min-cheom as his deputy and, according to the Goryeosa, led 208,300 men. At Heunghwajin he blocked a stream east of the fortress with thick ropes threaded through cowhides, hid 12,000 horsemen in the hills and, when the Khitans came, broke the dam and sprang the ambush. Xiao Paiya nevertheless pressed on towards the capital; on 10 February his army was only 100 li from Gaegyeong, but the king had the countryside emptied, and the harassed Khitans turned back. On 10 March, as they passed Gwiju, Kang's army attacked east of the town. The fight hung in the balance until reinforcements under Kim Jong-hyeon arrived and a wind and rain from the south blew the banners northwards; the Khitans broke and were pursued across the Seokcheon river to Panryeong. The Goryeosa says the fields were covered with corpses and only a few thousand returned alive, and that the Liao emperor threatened to flay Xiao's face before executing him.

Kang returned in triumph; King Hyeonjong met him at a post station, personally set eight golden flowers in his hair and renamed the station. The History of Liao records only, under the twelfth lunar month, a defeat at the Cha and Tuo rivers in which many soldiers of two guard armies drowned, and says that in spring 1019 Xiao Paiya and the other commanders were charged with misconduct of the war and pardoned. In 1020 Goryeo resumed sending tribute, and in 1022 the two states made peace: Goryeo acknowledged Liao overlordship and adopted the Liao era name — although the historian Hans Bielenstein argues that it kept its own era name and its contacts with the Song — and the Liao never invaded Korea again. On Kang's advice an outer wall was built around Gaegyeong. In Korean memory the battle ranks with Salsu and Hansan among the greatest victories in the country's history.