 In the beginning of the war, Thánh Tông and Nhân Tông had to order the army retreat to avoid the pressure from Yuan's force when Prince Chiêu Minh Trần Quang Khải commanded troops try to stop Sogetu's fleet in the Nghệ An Province.During this time, there were several high-ranking officials and members of royal family of the Trần dynasty defected to Yuan's side including Thánh Tông's own brother, Prince Chiêu Quốc Trần Ích Tắc and Trần Kiện who was son of Prince Tĩnh Quốc Trần Quốc Khang.For the safeness of Thánh Tông and Nhân Tông's retreat, Princess An Tư was offered as present and diversion for prince Toghan while Marquis Bảo Nghĩa Trần Bình Trọng was captured and later killed in Battle of Đà Mạc in defending the two emperors.