This heterogeneous group of peoples distributed north and south of the lower Kasai River, its tributaries, and the lower Congo River as far as Kinshasa all speak Bantu languages more closely related to each other than to those of adjacent peoples. Many of these groups, particularly those at the periphery, have been influenced by adjacent peoples--the Mongo in the north and peoples of the Kwango River in the southwest.

Vansina has distinguished several clusters, each including the group giving its name to the cluster and others. The Tio cluster includes the core peoples of the Tio Kingdom and several others, some of them never incorporated into the kingdom. The Boma-Sakata cluster includes the Nku and several smaller groups. The Yans-Mbun cluster includes a number of smaller entities. The Kuba cluster includes the Leele, the Njembe, and a number of groups governed by a ruling group called the Bushong, together called Kuba.

The Tio Kingdom was established along both sides of the Congo River north and south of Stanley Pool (now Pool de Malebo) at least as early as the fifteenth century and influenced the development of smaller kingdoms and chiefdoms along the lower Kasai thereafter. At the eastern end of the region, the kingdom of the Kuba, already in existence but not well developed, was reorganized in the midseventeenth century and exercised considerable influence in the region west of the Tshiluba-speaking peoples. Between the Tio in the west and the Kuba, most of the peoples in the region were organized into small kingdoms or chieftainships that extended beyond the level of the village or local community. The only important exception was the Leele. There were Leele chiefdoms, but the chiefs had no real significance, and the villages were essentially autonomous and often in conflict.

Local communities were governed by local chiefs in almost all cases. There were superior chiefs nearly everywhere and, in three cases at least, kings, but their powers were often limited. In the cases of kingdoms, one task of the superior chief was to collect tribute.

The Tio Kingdom was large but decentralized. One of the segments in what is now Zaire was essentially autonomous, paying tribute to the king irregularly. The other was more closely controlled, and in certain legal cases, appeals to the king from the judgments of the local chief were possible. The Kuba Kingdom was much more tightly organized. In Vansina's view, this was perhaps the most complex state organization in Zaire with the exception of the Lunda Empire.

Data as of December 1993