The Vietnamese kingdom of Đại Việt, concerned with their rival Champa to the south sought a clearly defined border with the growing power of Fa Ngum. The result was to use the Annamite Range as both a cultural and territorial barrier between the two kingdoms. Continuing his conquests Fa Ngum turned toward the Sip Song Chau Tai along the Red and Black River valleys, which were heavily populated with Lao. Having secured a sizable force of Lao from each territory under his domain Fa Ngum moved down the Nam Ou to take Muang Sua. Despite three attacks the King of Muang Sua, who was Fa Ngum's uncle, was unable to deter the size of Fa Ngum's army and committed suicide rather than be taken alive.