However, the tension between Goryeo and Liao created another war. In 1009, General Gang Jo of Goryeo led a coup against King Mokjong, killing the king and establishing military rule. In 1010, the alliance was broken and Liao attacked Goryeo for General Gang's treason. Also, the Liao claimed six garrison settlements east of the Yalu River, which Goryeo claimed as its territory in truce negotiations during 993. After suffering numerous and heavy casualties against the Goryeo army, the Liao dynasty managed to defeat Gangjo, who had begun to underestimate them. Despite this defeat, the Goryeo king managed to retain his claim on the six garrison settlements. The Liao forces retreated from the peninsula, with no great prize for the war, but they did not give up their hope of gaining the six garrison settlements and making Goryeo pay tribute.