During the Southern Song dynasty the descendant of Confucius at Qufu, the Duke Yansheng Kong Duanyou fled south with the Song Emperor to Quzhou, while the newly established Jin dynasty (1115–1234) in the north appointed Kong Duanyou's brother Kong Duancao who remained in Qufu as Duke Yansheng. From that time up until the Yuan dynasty, there were two Duke Yanshengs, once in the north in Qufu and the other in the south at Quzhou. During the Yuan dynasty, the Emperor Kublai Khan invited the southern Duke Yansheng Kong Zhu to return to Qufu. Kong Zhu refused, and gave up the title, so the northern branch of the family kept the title of Duke Yansheng. The southern branch still remained in Quzhou where they lived to this day. Confucius's descendants in Quzhou alone number 30,000. During the Yuan dynasty, one of Confucius' descendants moved from China to Goryeo era Korea and established a branch of the family there after marrying a Korean woman.
What did Kong Zhu decide against?