The First Goryeo-Khitan War was a 10th-century conflict between the Goryeo dynasty of Korea and the Khitan-led Liao dynasty of China near what is now the border between China and North Korea. In 993, the Liao dynasty invaded Goryeo's northwest border with an army that the Liao commander claimed to number 800,000. They forced Goryeo to end its tributary relations with the Song dynasty, to become a Liao tributary state and to adopt Liao's calendar. With Goryeo's agreement of these requirements, Liao forces withdrew. The Liao dynasty gave Goryeo permission to incorporate the land along the border of the two states, which was occupied by Jurchen tribes that were troublesome to Liao, up to the Yalu River. In spite of the settlement, Goryeo continued to communicate with the Song dynasty, having strengthened its defenses by building fortresses in the newly gained northern territories.