Which best describes forces that shaped pre-colonial africa?

The only force that we can say shaped pre-colonial Africa is the military force. Have in mind that One purpose of centralized political systems was to create the foundation for large military forces that could be called upon for defense and territorial expansion and actualy authoritarianism and the use of force were dominant features of European colonial administrations in Africa. 
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More than 4 million enslaved hunan beings in the south and they touched every aspect of the regions social, political and economic life.