In 979, Emperor Đinh Tiên Hoàng and his crown prince Đinh Liễn were assassinated by Đỗ Thích, a government official, leaving his lone surviving son, the 6-year-old Đinh Toàn, to assume the throne. Taking advantage of the situation, the Song dynasty invaded Đại Cồ Việt. Facing such a grave threat to national independence, the commander of the armed forces, (Thập Đạo Tướng Quân) Lê Hoàn took the throne, replaced the house of Đinh and established the Early Lê dynasty. A capable military tactician, Lê Hoan realized the risks of engaging the mighty Song troops head on; thus, he tricked the invading army into Chi Lăng Pass, then ambushed and killed their commander, quickly ending the threat to his young nation in 981. The Song dynasty withdrew their troops and Lê Hoàn was referred to in his realm as Emperor Đại Hành (Đại Hành Hoàng Đế).^[126] Emperor Lê Đại Hành was also the first Vietnamese monarch who began the southward expansion process against the kingdom of Champa.