Historians and economists have increasingly identified capitalist patterns of behavior among antebellum slave owners, yet no consensus has emerged about the explanation for this finding. I argue that US slave owners were driven to behave like capitalists in part because of their dependence on credit. The ability of creditors to seize the land and slaves of insolvent debtors generated selection pressures that led to both aggregate patterns of capitalist development and the adaptation of individual slave owners to the logic of capitalist competition. I refer to this process as “credit market discipline.” In a case study of South Carolina in the 1840s, I show that the threat and reality of foreclosure was capable of stimulating recognizably capitalist behaviors among even the most aristocratic and “prebourgeois” slave owners.