General Yi Songgye
In its decline the Koryo court faced another problem besides the ouster of their Mongol overlords. Japanese pirates were attacking and robbing coastal areas, leaving large areas of the coast depopulated. Korea initi-ated military campaigns against the pirates in which two powerful gen-erals emerged—Yi Songgye (1335–1408) and Choe Yong (1316–88). The two, who were both successful in the Japanese campaigns, also proved pivotal in the new fights on the Chinese front.
The new Ming court was not as loyal to Koryo as Koryo was to Ming. Koryo was quick to recognize the Ming as the rightful successor to the alien Yuan dynasty.
The Ming court, however, was suspicious of its “little brother,” a loyal tributary among the barbarians. Ming laid claim to the territory the Yuan had held in the northern part of the peninsula. Koryo counterclaimed the territory, which it had held prior to the Yuan confiscation.
The two generals, Choe and Yi, differed on how to deal with the problem. Choe wanted to attack the Ming forces to the north of Korea, while Yi opposed the attack. However, King U (r. 1374–88) chose to attack, and as a kind of test of loyalty he put Yi in charge of the expedi-tion. Yi obediently led the march north.
In the middle of the Yalu River, on the islands in the estuary of the river, Yi Songgye was caught in the mid-summer monsoon rains, and there he made a momentous deci-sion. He decided it would be better to take over the kingdom of Koryo rather than pursue a basically suicidal mission against the Ming. He turned his forces around and successfully marched on Kaesong. The year was 1388.
For the next four years Yi controlled the court from behind the scenes. He deposed King U and installed U’s son, Chang (r. 1388–89). Then, claiming that King Chang was tainted by Mongol blood, Yi placed King Kongyang (r. 1389–92) on the throne, a distant royal relative who was descended from an early Koryo king. Yi banished his military rival, Choe Yong, and then had him executed. He was paving the way for the establishment of a new ruling dynasty.
New dynasties in Korea were rare. The Koryo dynasty had survived a military coup and the Mongol invasion, and it was in the process of recovering from the fall of the Yuan dynasty. To set up a new dynasty was potentially a violation of tributary agreements with China, and it was certainly a violation of Confucian ethics: “There is only one sun in the sky; there is only one king on the throne.” Yi Songgye’s new dynasty had to be set up very carefully. When he proclaimed the new dynasty four years later, in 1392, he set up a line of rulers that was to last for 518 years. Only the third of the Korean dynasties, it was also to be the last.