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Goryeo-Jurchen War

The Jurchens in the Yalu River region were tributaries of Goryeo since the reign of Taejo of Goryeo (r. 918-943), who called upon them during the wars of the Later Three Kingdoms period. Taejo relied heavily on a large Jurchen cavalry force to defeat Later Baekje. The Jurchens switched allegiances between Liao and Goryeo multiple times depending on which they deemed the most appropriate. The Liao and Goryeo competed to gain the allegiance of Jurchen settlers who effectively controlled much of the border area beyond Goryeo and Liao fortifications. These Jurchens offered tribute but expected to be rewarded richly by the Goryeo court in return. However the Jurchens who offered tribute were often the same ones who raided Goryeo's borders. In one instance, the Goryeo court discovered that a Jurchen leader who had brought tribute had been behind the recent raids on their territory. The frontier was largely outside of direct control and lavish gifts were doled out as a means of controlling the Jurchens. Sometimes Jurchens submitted to Goryeo and were given citizenship. Goryeo inhabitants were forbidden from trading with Jurchens.

The tributary relations between Jurchens and Goryeo began to change under the reign of Jurchen leader Wuyashu (r. 1103–1113) of the Wanyan clan. The Wanyan clan was intimately aware of the Jurchens who had submitted to Goryeo and used their power to break the clans' allegiance to Goryeo, unifying the Jurchens. The resulting conflict between the two powers led to Goryeo's withdrawal from Jurchen territory and acknowledgment of Jurchen control over the contested region.

As the geopolitical situation shifted, Goryeo unleashed a series of military campaigns in the early 12th century to regain control of its borderlands. Goryeo had already been in conflict with the Jurchens before. In 984, Goryeo failed to control the Yalu River basin due to conflict with the Jurchens. In 1056, Goryeo repelled the Eastern Jurchens and afterward destroyed their stronghold of over 20 villages. In 1080, Munjong of Goryeo led a force of 30,000 to conquer ten villages. However by the rise of the Wanyan clan, the quality of Goryeo's army had degraded and it mostly consisted of infantry. There were several clashes with the Jurchens, usually resulting in Jurchen victory with their mounted cavalrymen. In 1104, the Wanyan Jurchens reached Chongju while pursuing tribes resisting them. Goryeo sent Im Gan to confront the Jurchens, but his untrained army was defeated, and the Jurchens took Chongju castle. Im Gan was dismissed from office and reinstated, dying as a civil servant in 1112. The war effort was taken up by Yun Kwan, but the situation was unfavorable and he returned after making peace.

Yun Kwan believed that the loss was due to their inferior cavalry and proposed to the king that an elite force known as the Byeolmuban (別武班; "Special Warfare Army") be created. It existed apart from the main army and was made up of cavalry, infantry, and a Hangmagun ("Subdue Demon Corps"). In December 1107, Yun Kwan and O Yŏn-ch’on set out with 170,000 soldiers to conquer the Jurchens. The army won against the Jurchens and built Nine Fortresses over a wide area on the frontier encompassing Jurchen tribal lands, and erected a monument to mark the boundary. However due to unceasing Jurchen attacks, diplomatic appeals, and court intrigue, the Nine Fortresses were handed back to the Jurchens. In 1108, Yun Kwan was removed from office and the Nine Fortresses were turned over to the Wanyan clan. It is plausible that the Jurchens and Goryeo had some sort of implicit understanding where the Jurchens would cease their attacks while Goryeo took advantage of the conflict between the Jurchens and Khitans to gain territory. According to Breuker, Goryeo never really had control of the region occupied by the Nine Fortresses in the first place and maintaining hegemony would have meant a prolonged conflict with militarily superior Jurchen troops that would prove very costly. The Nine Fortresses were exchanged for Poju (Uiju), a region the Jurchens later contested when Goryeo hesitated to recognize them as their suzerain.

Later, Wuyashu's younger brother Aguda founded the Jin dynasty (1115–1234). When the Jin was founded, the Jurchens called Goryeo their "parent country" or "father and mother" country. This was because it had traditionally been part of their system of tributary relations, its rhetoric, advanced culture, as well as the idea that it was "bastard offspring of Koryŏ". The Jin also believed that they shared a common ancestry with the Balhae people in the Liao dynasty. The Jin went on to conquer the Liao dynasty in 1125 and capture the Song capital of Kaifeng in 1127 (Jingkang incident). The Jin also put pressure on Goryeo and demanded that Goryeo become their subject. While many in Goryeo were against this, Yi Cha-gyŏm was in power at the time and judged peaceful relations with the Jin to be beneficial to his own political power. He accepted the Jin demands and in 1126, the king of Goryeo declared himself a Jin vassal (tributary). However the Goryeo king retained his position as "Son of Heaven" within Goryeo. By incorporating Jurchen history into that of Goryeo and emphasizing the Jin emperors as bastard offspring of Goryeo, and placing the Jin within the template of a "northern dynasty", the imposition of Jin suzerainty became more acceptable.