In a classic study by the late E. E. Evans-Pritchard (1940), Nuer political life was characterized as a system of fission and fusion. Lineage groups would bind together in some instances, and, in principle, the Nuer could conceive of all distinct descent groups uniting in this fashion. When disputes were localized, segmentation between smaller patrilineal groups would occur. Localized disputes, theft, or homicide were mediated by individuals called kwar (chiefs), whose words were effective because of their authority rather than their overt power. Chiefs could settle a dispute only once those in conflict agreed to a settlement. The introduction of secular chiefs and courts irrevocably changed traditional custom and usage.