But Africans were living in all kinds of conglomerations, from small villages to city-states to empires, and they were much too powerful for the Europeans to just conquer. And in fact, Europeans obtained African slaves by trading for them. Because trade is a two-way proposition, this meant that Africans were captured by other Africans and then traded to Europeans in exchange for goods, usually like metal tools or fine textiles or guns. And for those Africans, slaves were a form of property, and a very valuable one. In many places, slaves were one of the only sources of private wealth because land was usually owned by the state. And this gets to a really important point. If we're going to understand the tragedy of slavery, we need to understand the economics of it.