In 993, the Liao dynasty invaded Goryeo's northwest border with an army that the Liao commander claimed to number 800,000, demanding Goryeo cede territories along the Yalu River.[2][7] Goryeo appealed for assistance from the Song dynasty, with whom they had a military alliance, but no Song assistance came. After the initial battles, the Khitans made steady southward progress before reaching the Cheongcheon River, at which point they called for negotiations with Goryeo military leadership. While the Khitans initially demanded total surrender from Goryeo, and Goryeo initially appeared willing to consider it, Sŏ Hŭi was eventually able to convince the Khitans to accept Goryeo as a tributary state instead. By 994, regular diplomatic exchanges between the Khitans and Goryeo began.[8]
They forced Goryeo to end its tributary relations with the Song dynasty, to become a Liao tributary state and to adopt Liao's calendar.[1][2][3][4][5][6] 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.[9][10] In spite of the settlement, Goryeo continued to communicate with the Song dynasty,[11] having strengthened its defenses by building fortresses in the newly gained northern territories.[2]
^ abHatada, Smith Jr & Hazard 1969, p. 52: "In the thirteenth year of the reign of King Sŏngjong (994), Koryŏ submitted to the Khitan and adopted their calendar".
^ abEbrey & Walthall 2014, [1], p. 171, at Google Books: Liao forces invaded Goryeo territory in 993. Instead of pushing for total victory, the Khitans negotiated a peace that forced Goryeo to adopt the Liao calendar and end tributary relations with Song (a violation of King Taejo’s testamentary injunction never to make peace with the Khitan)."
^ abSimons 1995, p. 95: "In 994, during the reign of King Songjong, Koryo was forced to acknowledged the dominance of Khitan".
^Yun 1998, p.64: "By the end of the negotiation, Sŏ Hŭi had ... ostensibly for the purpose of securing safe diplomatic passage, obtained an explicit Khitan consent to incorporate the land between the Ch’ôngch’ôn and Amnok Rivers into Koryô territory."
^Twitchett & Tietze 1994, p.102: "Until the 980s Khitan-Koryǒ relations had been at arm’s length, for the Jurchen tribes and Ting-an had provided a buffer zone between Koryǒ's northern frontier and the Liao border". p.103: "Koryǒ was left free to deal with the Jurchen tribes south of the Yalu Valley".
^Hyun 2013, p.106: "Even though the Goryeo court agreed to set up tribute exchanges with the Liao court, that same year [=994] it also sent an envoy to the Song court to appeal, but in vain, for military assistance against the Khitan."
References
Ebrey, Patricia Buckley; Walthall, Anne (2014), Pre-Modern East Asia: To 1800: A Cultural, Social, and Political History, Third Edition, Boston, MA: Wadsworth, Cengage Learning, ISBN978-1-133-60651-2.
Hatada, Takashi; Smith Jr, Warren W.; Hazard, Benjamin H. (1969), A History of Korea, Santa Barbara, CA: ABC-Clio, ISBN0-87436-064-1.
Hyun, Jeongwon (2013), Gift Exchange among States in East Asia during the Eleventh Century (Thesis (Ph.D.)), University of Washington, hdl:1773/24231.
Nahm, Andrew C. (1988), Korea: Tradition & Transformation: A History of the Korean People, Elizabeth, NJ: Hollym, ISBN0-930878-56-6.
Twitchett, Denis; Tietze, Klaus-Peter (1994), "The Liao", in Franke, Herbert; Twitchettr Denis (eds.), The Cambridge History of China, Volume 6, Alien Regime and Border States, 907-1368, Cambridge: Cambridge University Press, pp. 43–153, ISBN0-521-24331-9.
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