Imagine a time and place where a small debt—even just a few dollars—could translate into a lifetime of servitude not only for the debtor, but also for his or her children. For much of the 19th century, the American Southwest was just such a place. There, a system commonly called debt peonage relegated thousands of men, women, and children to years of bondage to a master.

This system of unfree labor came into existence in the 1700s, when the region was …