Trần Thái Tông
In 1258, the Vietnamese monarch Trần Thái Tông commenced regular diplomatic relations and a tributary relationship with the Mongol court, treating them as equals to the embattled Southern Song dynasty without renouncing their ties to the Song. In March 1258, Trần Thái Tông retired and let his son, prince Trần Hoảng, succeed the throne. In the same year, the new king sent envoys to the Mongol in Yunnan. The Mongol leader Uriyangkhadai demanded that the king come to China to submit in person. King Trần Thánh Tông answer: "If my small country sincerely serves your majesty, how will your big country treat us?" The Mongol envoys traveled back to Thăng Long, Yunnan and Dadu, eventually the message from the Vietnamese court was that the king's children or brother would be sent to China as hostage.