The reason why traditional African societies are characterized as "anarchies" is because of their horizontal political structure and absence of classes. In addition to that leadership of elders normally did not transcend into the authoritative structure, which characterizes the modern state (see also Pierre Clastres' thesis expounded in Society Against the State).
A strong value was however placed on traditional and "natural" values. So for example, although there were no laws against rape, homicide, and adultery, a person committing those acts would be persecuted together with his or her kin. The principle of collective responsibility was sometimes upheld.
Starting in the 15th century the class system began to form in the last empires of Africa, although it had already existed in some African civilizations (such as Nubia, Egypt, Axum and Hausa) for millennia. However, many societies have until this day remained as what is called “tribes without rulers”, a form of “ordered anarchy”.