Which statement best completes the timeline? The Goryeo dynasty swears allegiance to the Mongol Empire. Korea becomes isolated during the Joseon dynasty Korea modernizes under Emperor Gojong. O A. Japan makes Korea part of its growing empire. OB. Korea is split into North Korea and South Korea. O C. Russia supports communist groups in Korea. O D. Korea is divided during the Three Kingdoms period. can someone answer me what happened before the goryeo dynasty sweared to allie with the mongol empire.​