Rules of Royal Succession in the Early Period of Koguryŏ and King Ch’adae’s Coup d'état

This paper analyzed the process of King Ch’adae (Susŏng)’s accession to the throne, which was understood as one of the coups in the Early Period of Koguryŏ, and discussed the correlation with the rules of royal successions. First, it examined previous studies about the rules of royal successions in this period, as well as various issues related to this. Although discussion is still required to define 'sibling succession' as the basic rule or principle of royal successions in this period, this paper viewed that paternal succession was the basic principle of royal succession. Also, levirate in Koguryŏ, which was understood as a tradition closely related to sibling succession, was in fact a custom to supplement paternal succession of the royal family in a broad sense. The crucial and distinct element of levirate was that children between the union of younger brother and sister-in-law was considered as the heir of dead brother. Therefore, even if a king’s younger brother succeeded the throne, the dead elder brother’s son was to succeed the throne after the younger brother. Susŏng, the younger brother of King T’aejo, was also supposed to succeed the throne but hand the throne to King T’aejo’s sons in order to maintain the lineage of his brother. Susŏng’s coup d'état was, in this sense, to forcibly take the throne and secure the royal lineage that would continue to his direct descendants.