In 1257, Crown Prince Trần Hoảng witnessed the first Mongol invasion in Vietnam. In the beginning, Đại Việt's army suffered several defeats by the Mongols, who had already conquered a vast area in Asia. Several high-ranking officials of the Trần dynasty were so frightened 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 Song China. But because of the firm faith of Emperor Thái Tông, Grand Chancellor Trần Thủ Độ, and the talents of generals such as Prince Hưng Đạo Trần Quốc Tuấn and Lê Phụ Trần, the Trần dynasty was able to repulse the invasion and ultimately re-establish peace in Đại Việt in December 1257.