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The Three Kingdoms period Samguk Sagi ( History of Three Kingdoms ) recorded that in 512 , the 13th reign year of King Jijeung of Silla , one of the Three Kingdoms of Korea , Gen. Isabu conquered the State of Usan ( Usan-guk ) , whence it submitted yearly tributes to the Silla court .
 Korea, Isabu
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Korea, Isabu