The Kmhmu once were masters of the domain of Muong Cvaa (or Muong Sua), centered on what is now the city of Luang Prabang. Following their conquest in the thirteenth century by Lao people, the Kmhmu were driven into remote mountain ranges or became serfs to a Lao aristocracy. In places, however, the Kmhmu retained a good deal of autonomy and local authority, sometimes even governing over local Lao and Tai populations. The Kmhmu were recognized as older brothers of the Lao and Tai in coronation ceremonies and other court rituals in Luang Prabang and Nan, and in oral traditions of the Lao and Kmhmu. In the nineteenth and twentieth centuries, Kmhmu frequently rebelled against the local Tai and Lao feudal lords and French colonial authorities, in millennarian rebellions that were called Sôk Cheuang (Cheuang's Wars), after the mythical or legendary culture hero Cheuang. From 1945 until 1975, Kmhmu were in the forefront of the Lao independence revolution, making up the largest part of the Neo Lao Hak Xat (Pathet Lao) military forces. A smaller segment of the Kmhmu population supported the United States and Royal Lao Government; many of them fled as refugees following the establishment of the Lao People's Democratic Republic in 1975.
Kmhmu share many cultural traditions with their Lao and Tai neighbors, and with other neighboring ethnic groups including the Lamet (Rmeet), Hmong, and Thin (Mai-Pray). These may include subsistence technology, crafts and material culture, music and song, and clothing. There are nevertheless cultural traditions unique to the Kmhmu, or borrowed from them by their neighbors. Intermarriage with members of other ethnic groups is not infrequent; in some cases non-Kmhmu people (especially those from smaller ethnic groups) marry into a Kmhmu village, adopting Kmhmu language and traditions, while in other cases Kmhmu marry out, taking on the language and traditions of another group (especially the larger Lao or Tai culture).