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Foreign relations

Goryeo affiliated itself with the successive short-lived Five Dynasties beginning with the Shatuo Later Tang dynasty in 933, and Taejo was acknowledged as the legitimate successor to Dongmyeong of Goguryeo.

In 962, Goryeo entered relations with the nascent Song dynasty. Song did not have real suzerainty over Goryeo, and Goryeo sent tribute mainly for the sake of trade. Later, Goryeo entered nominal tributary relations with the Khitan Liao dynasty then the Jurchen Jin dynasty while maintaining trade and unofficial relations with the Song dynasty. The Korean missions to China were intended to seek knowledge on fields such as Confucianism, Buddhism, history, and other subjects, conduct diplomacy, and trade. Missions to the Song in 976, 986, and after 1105 stayed there for study. Goryeo requested texts from the Song in 991, 993, 1019, 1021, 1073, 1074, 1092, and after 1105. They also brought texts to China. Diplomatic missions were conducted to announce birthdays, deaths, and successions. Trade, in particular, was an important aspect of all the missions. Annual tribute was expected to be exchanged for proper payment. In 1093, Su Shi suggested that Goryeo envoys should stick to trade in commercial products such as silk and hair instead of books. Sometimes missions were sent even though they would not be received to conduct trade.

The Five Dynasties, Song dynasty, and Jin dynasty pretended that Goryeo was a tributary vassal. However this was a fiction. The Five Dynasties and the Song did not share a border with Goryeo and had no way to assert supremacy over it. The Liao invasions of Goryeo from 993 to 1020 were successfully repelled. The Jin made no similar effort against Goryeo. Goryeo was not a vassal to these powers and successfully stood up to Liao and Jin through clever diplomacy and minimal appeasement. Goryeo was autonomous until Mongol rule. Sinologist Hans Bielenstein described the nature of Goryeo's nominal tributary relations with the dynasties in China:

The Five Dynasties, Sung, Liao, and Chin all liked to pretend that Koryŏ was a tributary vassal. Nothing could be more wrong. The Five Dynasties and Sung had no common border with Koryŏ and no way, even if they had possessed the military resources, to assert any supremacy over it. The Liao invasions of Koryŏ from 993 to 1020 were successfully repelled by the Koreans. The Chin made no serious attempts against Koryŏ. The dynastic historians accepted nevertheless the official fiction and referred to Koryŏ by an unrealistic terminology. To repeat, Koryŏ was not a vassal with tributary duties to the Five Dynasties, Sung, Liao, and Chin. In spite of its smaller size, it was able to stand up to Liao and Chin, and did not have to buy peace. This required clever diplomacy and a minimum of appeasement. In spite of window-dressing, rhetorics, and even a pinch of nostalgia for the good old times of Korean-Chinese friendship, Koryŏ succeeded in keeping its autonomy until the advent of the Mongols.

In 1270, Goryeo capitulated to the Yuan dynasty, which exercised a powerful influence over Goryeo affairs and the succession of Goryeo kings. Goryeo remained under the Yuan dynasty until the mid-14th century.

Goryeo used multiple calendars. In 938, it used the Later Jin calendar, in 948 Later Han, in 952 Later Zhou, in 963 Song, in 994 Liao, in 1016 Song, and in 1022 Liao. In 1136, Goryeo was presented with a Jin calendar. It is possible that Goryeo used different calendars simultaneously depending on which country they dealt with.