<P> In a time of relative peace and stability in the region, Balhae flourished, especially during the reigns of King Mun and King Seon . Balhae was called the "Prosperous Country in the East". However, Balhae was severely weakened and eventually conquered by the Khitan Liao dynasty in 926 . Large numbers of refugees, including Dae Gwang - hyeon, the last crown prince of Balhae, were welcomed by Goryeo . Dae Gwang - hyeon was included in the imperial family of Wang Geon, bringing a national unification between the two successor nations of Goguryeo . </P> <P> No historical records from Balhae have survived, and the Liao left no histories of Balhae . While Goryeo absorbed some Balhae territory and received Balhae refugees, it compiled no known histories of Balhae either . The Samguk Sagi ("History of the Three Kingdoms"), for instance, includes passages on Balhae, but does not include a dynastic history of Balhae . The 18th century Joseon dynasty historian Yu Deukgong advocated the proper study of Balhae as part of Korean history, and coined the term "North and South States Period" to refer to this era . </P> <P> The Later Three Kingdoms (900--936 CE) consisted of Silla, Hubaekje ("Later Baekje"), and Taebong (also known as Hugoguryeo, "Later Goguryeo"). The latter two, established as Later Silla declined in power, claimed to be heirs to Baekje and Goguryeo . </P> <P> Taebong (Later Goguryeo) was originally led by Gung Ye, a Buddhist monk who founded Later Goguryeo . Gung Ye was actually a son of King Gyeongmun of Silla . When Gung Ye was born, there was an omen that he would be a cause of Silla's downfall, and thus Gyeongmun ordered his newborn to be killed . Gung Ye's nurse however, ran away with him and raised him . The unpopular Gung Ye was deposed by Wang Geon in 918 . Wang Geon was popular with his people, and he decided to unite the entire peninsula under one government . He attacked Later Baekje in 934 and received the surrender of Silla in the following year . In 936, Goryeo conquered Hubaekje . </P>

The only contemporary written account of the first korean state the choson kingdom comes from