Excerpts from Books and Wikipedia
"The period of Korean history between the first century B.C.E. and the seventh century C.E. is known as the 'Three Kingdoms' period. At this time Korea was divided into four parts. The northwest was under Chinese occupation, and the rest was fought over by three native kingdoms: Koguryo, Paekche, and Silla. . . . China allied with Silla, the second-strongest kingdom. The allies conquered Paekche in 660 and Koguryo in 668, uniting the peninsula under a single ruler for the first time. The Chinese assumed the united Korea would be a vassal state and began to garrison the country. However, Munmu, rebelled and fought for eight years to establish Silla's dominance. Silla retained its dominance until 892 when Paekche regained its independence. In 901, Kungye, a rebel prince, revived the kingdom of Koguryo, which in 918 was renamed Koryo ( or Korea) by King Wang Kon." [1001 Days]