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Usan-guk, or the State of Usan, occupied Ulleung-do and the adjacent islands during the Korean Three Kingdoms period. According to the Samguk Sagi, it was conquered by the Silla general Kim Isabu in 512. He is said to have used wooden lions or tigers to intimidate the residents into surrendering. Usan-guk rarely enters into historical records, but appears to have continued a largely autonomous existence until its annexation to Goryeo in 930.
According to Sejong Sillok, Goryeosa, and Mangi Yoram, Usan-guk consisted of Ulleung-do and Usan-do. Koreans believe Usan-do is the Liancourt Rocks (Dokdo in Korea, Takeshima in Japan), although some Japanese scholars dispute the interpretation of some of the records.
Old Korean maps
A map by Korean Empire:Ulleungdo(鬱陵島) and Usan(于山)