Well just like stealing war and all the vices associated with human slavery began with the dawn of civilization, to be more specific it began in Africa during the growth of the great ancient Egyptian civilization. There is normally a Misconception that Europeans brought slavery to African but it is not true, even if the question is directed towards Sub Saharan African, there was a slave trade in existence long before the arrival of the Europeans although they cam to economize and perpetuate the slave trade towards their own selfish gains to build the so called New World. Before their arrival slaves were only people who were caught in a criminal act so they will be sentenced to be slaves for some years and after return to doing whatever they did before that.