Vieng Phoukha was also prospering by the 17th century, with the construction of dozens of Buddhist monasteries and pagodas in the Nam Jook and Nam Fa River valleys. Evidence of what must have been a large population in Vieng Phoukha can be seen just north of the district capital, where an extensive khou vieng (earthen rampart) surrounds the ruins of sprawling Vat Mahaphot and many smaller pagodas.

Though Muang Houa Tha enjoyed peace and stability through most of the 17th century, beginning in 1709 a series of natural disasters weakened the Muang and it briefly came under the influence of the Sipsongpanna Kingdom centered in southern China. A population exodus to Muang Sing, Muang Nan (Thailand) and Muang Ngern (Sayabouli Province) ensued, eventually causing the Nam Tha Valley to become nearly completely abandoned for 155 years. During the late 1700’s prior to the reign of Chao Fa Silinor, one of the first main population movements into Muang Sing began with a group of Tai-Lue from Xieng Khaeng, led by a woman named Nang Khemma. Nang Khemma was the widow of Xieng Khaeng’s ruler at the time and went on to commission the construction of That Xieng Teung Stupa in 1787. Today, That Xieng Teung remains highly revered by Tai-Lue Buddhists throughout the region and is believed to contain a sacred relic of the Lord Buddha.

In 1890, the Tai-Yuan returned to the Nam Tha Valley under the aegis of Chao Luangsitthisan to re-establish Muang Houa Tha. Vat Luang Korn, one of Luang Namtha’s largest, was constructed shortly thereafter in 1892. However, the newly resettled Muang Houa Tha was to enjoy its independence for only two years. In 1894, following a meeting between the French, British and Siamese colonists, it was agreed that Muang Houa Tha would be administered by the French and the Mekong from the northern reaches of Muang Sing to Chiang Saen would serve as the border between French Indochina and British-ruled Burma. Not long after this divide took place the first group of Tai-Dam arrived from Sip Song Chou Tai in north western Viet Nam and established Tong Jai Village on the east bank of the Nam Tha River. At about the same time the Tai-Dam arrived, migrations of Tai-Neua, Tai-Kao, Akha, Lanten, Yao and Lahu originating in Sipsongpanna, Burma and northwest Viet Nam began to migrate to the area’s fertile valleys and the forested mountains surrounding them.