 In 1258, the Trần Dynasty had to face the first Mongol invasion.In the beginning, the Đại Việt army suffered several defeats by an overwhelming force which had already conquered vast areas of Asia.Several high-ranking officials of the Trần Dynasty were so scared that Prince Khâm Thiên Trần Nhật Hiệu, younger brother of Thái Tông, even suggested to the Emperor that they might escape from Đại Việt to the Song Empire.