Common mistake; "African cichlids" as Andrew pointed out includes both lake and river cichlids. Additionally, in lake cichlids you have Haps, Peacocks, and Mbuna and generally for beginners it is advised not to mix these. Additionally some Mbuna such as the auratus and the johanni are much more aggressive than other Mbuna and a single specimen of these species will dominate a tank and kill off other species. Keeping and breeding Africans requires much more than just a general knowledge of preferred temperature, pH and general water parameters, thus they are recommended for advanced aquarium keepers rather than novice aquarium keepers.
Unfortunately many people getting into cichlids or Africans without being aware of all of this and so they end up with tanks of mixed cichlids or mixed African which often go south over the course of the first couple years, if not the first six months.