Koryo Dynasty's Use of Name North Yuan and Cognitions of East Asia -Focusing on Koryo Dynasty's Double-sided diplomacy-

The replacement of Yuan Dynasty by Ming Dynasty at the end of the 14th century meant that East Asia returned to plural order. From such a point of view, King Gongmin of the Koryo Kingdom was not the one who followed simple diplomacy of 'against Yuan and pro Ming'. At two-sided diplomacy under international situation that Yuan was replaced by Ming, King Gongmin adopted practical diplomatic policy by double-sided. After the fall of Yuan, East Asia kept power balance of North Yuan, Ming and Koryo Kingdom by remaining force of Yuan during a certain period so that Ming Dynasty only could not govern East Asia easily. The findings were as follow:Firstly, in 1356, 'Murder case of Gi Family' started to take special innovation actions of King Gongmin's policy that did not follow anti-Yuan policy. In the middle of the 14th century, Yuan was losing power, and it still kept its position of suzerain of giant power of Mongolia so that King Gongmin was unable to escape from system of Mongol Empire. Secondly, King Gongmin's declaration of North Yuan did not mean simple line diplomatic route. The Koryo Kingdom's declaration of North Yuan meant not severance of diplomatic relations with North Yuan but start of the relations with Ming. In 1369, the Koryo Kingdom broke off diplomatic relations with North Yuan in appearance and actually got in touch with North Yuan. King Gongmin opened diplomatic relations with Ming and also kept constant relations with North Yuan to seek for double-sided and practical diplomacy. Thirdly, diplomatic relations between Koryo and Ming was broken down because of Koryo to a certain degree. In 1371, Ming was consecutively defeated at the fighting against North Yuan so that it thought that Koryo informed North Yuan of situation in the name of dispatch of an envoy. The theory of Koryo's involvement in Nagachü's attack against Niujiazhuang(牛家莊) is thought be appropriate to a certain degree from point of view of King Gongmin's diplomatic route at that time. The Koryo Kingdom severed diplomatic relations with Ming in 1374 to let Ming make change of attitudes toward Koryo in 1377 that occurred not by changes of internal situation of both countries but by practical diplomacy of Koryo. Considering East Asia' return to plural world, Koryo accepted North Yuan's demand and had no idea to build up allied force: On the contrary, Koryo wanted to communicate with not only North Yuan but also Ming by resumption of diplomatic relations with Ming.