He's (Obama) wrong. Slavery wasn't per se an abuse of capitalism, but more an abuse of mercantilism. Slavery wasn't practiced widely on an individual basis. That is, slave owners were the equivalent of modern-day agribusiness and big corporations. It ran on the theory that wealth was power and that the purpose of agribusiness--the primary user of slaves--was to supply raw goods and materials to the home country for exploitation on the world market.
If the antebellum South in the US, for example, was capitalist rather than mercantilist, they would have closed the chain of manufacturing and trade to go from a raw material like cotton, to finished textiles and clothing. But they didn't. Cotton was for export almost exclusively, be it to Northern states where capitalists would manufacture it into finished products and then trade those, or to countries like England that did the same thing.
The same went for other Southern and Caribbean agricultural staples like, tobacco, sugar, cattle, citrus, and the like. None of these stayed local to be turned into end products. They were shipped elsewhere for that purpose. Mercantilism also generated monopolies, or near monopolies, where government(s) colluded with the wealthy owners to produce exclusive trade agreements that kept newcomers out of the market.
Mercantilism exploits local resources without generating a wide base of wealth. Instead, a small number of persons with great wealth gain from the exploitation while the local economy and most people in it stagnate in poverty. When the resources run out, the wealthy leave and the vast majority of the population is abandoned to their fate without care.
Capitalism invests in the local economy along with exploiting resources. It generates a wide base of income for a much larger portion of the population. This is why the North grew wealthy while the South stagnated economically.
