A form of stateless political organisation in which kin groups nest inside larger groups; segments that compete at one level unite against outsiders at a higher level, so order rests on balanced opposition rather than a ruler.
In more detail
The model was developed by E. E. Evans-Pritchard in The Nuer (1940) and generalised in African Political Systems (1940) and Tribes Without Rulers (1958). It explains how feuds can be contained without courts: allies and mediators are defined by genealogical distance, and compensation in cattle settles injuries. It has also been applied to Somali clans and Bedouin tribes. Later anthropologists criticised it as an idealised model that underestimated hierarchy, territorial ties and the influence of colonial rule.