The paradox is notable. Spain was as constant in support of slavery as it was in support of sanctuary. Madrid held a position not unlike Adam Smith’s: Slavery was an evil, a violation of natural law and reason. But as an established historical institution, it would be difficult if not impossible to extirpate. The demands of imperial security reconciled opposites. Starting in the last decades of the 1700s and continuing through 1816, Spanish troops in Northern Mexico captured thousands of “indios enemigos”—mostly Apache and Comanche warriors—and exiled them to Cuba as slaves. At the same time, the Crown repeatedly affirmed the humanity of slaves in terms that echoed Las Casas. Any enslaved person from another polity who entered the Spanish realm was made free, protected from being handed back to his or her master. Asylum seekers would be considered “vassals” of the monarchy and eligible for whatever employment they could find, as affirmed by a 1789 royal edict. When word spread of this order, enslaved people began fleeing the United States, crossing the Mississippi into Spanish Mexico. United States slavers complained that Spanish officials were using “every means to reduce, weaken and ruin the adjoining Country belonging to the Americans,’’ including encouraging “the desertion of slaves.’’

— America, América by Greg Grandin