 With military action in close proximity to Goryeo territory , coupled with a cancelled Liao invasion of Goryeo in 947 and a strong diplomatic and cultural relationship between the Goryeo and Song dynasties , Liao @-@ Goryeo relations were exceedingly poor . Both Liao and Goryeo saw each other as posing a military threat ; the Khitans feared that Goryeo would attempt to foment rebellions among the Balhae population in Liao territory , while Goryeo feared invasion by the Liao . The Khitans did invade Goryeo in 992 , sending a force that the Liao commander claimed to be 800 @,@ 000 strong , and demanding that Goryeo cede to territories along the Yalu River . Goryeo appealed for assistance from the Song dynasty , with which they had a military alliance , but no Song assistance came . The Khitans made steady southward progress before reaching the Ch 'ongch 'on River , at which point they called for negotiations between Liao and Goryeo military leaders . While the Liao initially demanded total surrender from Goryeo , and Goryeo initially appeared willing to consider it , the Korean negotiator was eventually able to convince the Khitans to accept a resolution in which the Goryeo dynasty became a tributary state to the Liao dynasty . By 994 , regular diplomatic exchanges between Liao and Goryeo began , and the relationship between Goryeo and Song irrevocably chilled . 
