Slate is running an excerpt from Wood's 2003 book Strange New Land: Africans in Colonial America as part of its course on American slavery.
Some people had experienced the first cold winds of enslavement well before 1650; others would escape the chilling blast well after 1700. The timing and nature of the change varied considerably from colony to colony, and even from family to family. Gradually, the terrible transformation took on a momentum of its own, numbing and burdening everything in its path, like a disastrous winter storm. Unlike the changing seasons, however, the encroachment of racial slavery in the colonies of North America was certainly not a natural process. It was highly unnatural—the work of powerful competitive governments and many thousands of human beings spread out across the Atlantic world. Nor was it inevitable that people’s legal status would come to depend upon their racial background and that the condition of slavery would be passed down from parent to child. Numerous factors combined to bring about this disastrous shift—human forces swirled together during the decades after 1650, to create an enormously destructive storm.
By 1650, hereditary enslavement based upon color, not upon religion, was a bitter reality in the older Catholic colonies of the New World. In the Caribbean and Latin America, for well over a century, Spanish and Portuguese colonizers had enslaved “infidels”: first Indians and then Africans. At first, they relied for justification upon the Mediterranean tradition that persons of a different religion, or persons captured in war, could be enslaved for life. But hidden in this idea of slavery was the notion that persons who converted to Christianity should receive their freedom. Wealthy planters in the tropics, afraid that their cheap labor would be taken away from them because of this loophole, changed the reasoning behind their exploitation. Even persons who could prove that they were not captured in war and that they accepted the Catholic faith still could not change their appearance, any more than a leopard can change its spots. So by making color the key factor behind enslavement, dark-skinned people brought from Africa to work in silver mines and on sugar plantations could be exploited for life. Indeed, the servitude could be made hereditary, so enslaved people’s children automatically inherited the same unfree status.