Historically, witchcraft in Africa has not comprised a stable or uniform set of beliefs. The idea of witchcraft, which might loosely be defined as the belief that people exist who use supernatural means to harm others, has existed in African societies from the precolonial, through the colonial, and into the postcolonial periods. But ideas about the kinds of powers that witches are alleged to use and the types of people often accused of using witchcraft have shifted in response to the changing political, economic, and social landscape. While witchcraft beliefs can sometimes be understood as metaphors for political forces and social ills, they must also be understood as separate systems of signs and meanings that have their own historical trajectories rooted in local cultures. Beliefs in witchcraft are beliefs in systems of power derived from unseen forces, and for those people who believe in supernatural powers those forces are quite real and are not merely metaphorical allusions to other phenomena. In the precolonial era, the political power that many chiefs and kings had was based in supernatural powers; these occult powers were potentially usable for either positive, socially accepted ends or for evil, selfish, and greedy ends. In the colonial and postcolonial eras, states and politicians have also been seen to have supernatural powers but are believed to have used them largely for self-enrichment or empowerment. Systems of global trade, including the trans-Atlantic slave trade and later colonial production of various commodities, both created wealth for a few and inflicted harm on many people. The perceived immorality of these economic and social networks was often captured in stories of witches ambushing people and selling them or consuming their life forces. The spiritual insecurity represented in these beliefs in witchcraft has continued into the postcolonial era.