Koguryo had been continually pursuing the endeavor of the external expansion for it's life and growth. The purpose of this research is to cast more light upon the subject of Koguryo’s Advance into Liao-tung(遼東). Truly, the fact that Koguryo occupy the Liao-tung Region is a well known. However, until now there has not been much analytical research into the Policy of Koguryo’s Advance into Liao-tung.
In order to do so, this research concentrate on explaining the Mo-yung Clan(慕容氏) and Koguryo in the fourth century. In this thesis, the matter on the consideration were divided into the following three parts.
1. The process by which Koguryo and the Mo-yung Clan take advantage of the decline of the Chin(晉), China and advance into Liao-tung is examined.
2. The conflict which arise when the borders of Koguryo and Mo-yung Clan meet as a result of the Mo-yung Clan´s Eastward Expansion into the Liao-tung Region are elucidate. After all, the Policy of Koguryo’s Advance into Liao-tung received a setback.
3. Koguryo’s domination of the declining Mo-yung Clan and the historic change in the occupation of the Liao-tung Region are examine. In the end, Koguryo completely dominate the Liao-tung Region by the latter half of the fourth century.