In 1564, the chronicle of Chiang Khaeng mentions Muang Sing in connection with an anti-Burmese uprising and an exodus. According to local tradition, the valley was recolonized in 1792 by Nang Khemma, the widow of the late ruler of Chiang Khaeng. Troubled by quarrels between her six sons, the widow moved with her son Cao Saengsi to Ban Nam Dai, a village about five km southwest of present-day Muang Sin. She founded Wiang Fa Ya, settled there and built a stupa on top of a mountain (That Chiang Tting, at the southern limit of the Muang Sin valley).

Subsequently, the Muang Sin kingdom vacillated between Chinese and Burmese influences, especially during the Buffalo War. In 1805, the region was devastated by a Siamese invasion to push back the plundering hordes of the Youennes (Yuan-Chinese), and many people were captured. The left bank of the Mekong was devastated, and large areas of territory deserted. In 1812, a second invasion resulted in the capture of 6,000 prisoners, and the devastation afflicting Muang Sin and the surrounding region continued. The people took refuge in the mountains and returned to Nam Ma valley (Introduction to the History of Müang Sing, Laos, prior to French Rule: the Fate of a Lü Principality by Volker Grabowsky, BEFEO, volume 86, pp. 233-291.1999).

From 1867-1868, French expeditions led by Doudard de Lagrée and Francis Garnier explored the area. Muang Sin’s precarious status was later revealed during secret negotiations between England and France to create a buffer state in the Upper Mekong region, with Muang Sin as its capital. When negotiations failed in 1895, the course of the Mekong north of Chiang Saen was defined as the border between British Burma and French Indochina.

In 1896, the French established a garrison at Muang Sin, and in 1904, the region became an autonomous principality under French protection after a new agreement between France and Great Britain. The Governor General of Indochina issued a decree in 1907 establishing a Government Commissioner delegate post in Muang Sin. In 1916, the kingdom became part of French Indochina, but the inhabitants contested the French occupation. During the first half of the 20th century, the French took advantage of the city’s strategic location by using it as a weigh station and market to regulate their monopoly on opium and exert control over the Hmong.

In 1962, Muang Sin valley was bombarded by the Pathet Lao, which destroyed most of the monasteries and sparked an exodus of the inhabitants towards Burma and Thailand. During the rest of the Secret War (1964-1975), the region remained in the hands of the Pathet Lao and reopened to the world in the 1990s.

The Lü country now can be discovered in the atmospheric villages of the Nam Ma valley and the splendid heights that extend towards the Nam Ha NBCA National Park