When I teach this subject in my class, it usually takes at least an entire class period to explain all the background properly. I will try to do it here as succinctly as possible, and then if you have additional questions or need clarifications, I will answer them.
First, you need to realize that slavery prior to 1400 was a very different institution compared to what it would become by 1600. Roman-style slavery had never completely died out in Europe. Roman slavery was very different than the race-based plantation style slavery that we’re used to reading about in the American Old South. In Roman-style slavery, slaves were acquired in two main ways. Either they were captured in a war, or they sold themselves into slavery to pay off a debt. It was not based on race. (In fact, the word “slave” comes from “Slav”, since the ancient Greeks used to capture and enslave Slavic peoples in the area north of Macedonia.) In both cases, the term of servitude was usually limited (5-10 years was common, although lifelong slavery did occur). Children of slaves were usually considered free persons. Slaves had the right to marry who they chose. Slaves also had the right to work outside the home after dark, so some of them could make money on the side. One guarantee that Roman slaves always had was that if they could earn their purchase price, they could automatically purchase their freedom. It was not uncommon for someone to start out as a slave, have the family work to buy the freedom of one person, and then they would work full time to free the rest. It was also frequent that someone would purchase their freedom and continue working for their master as a wage laborer. Manumission, or the granting of freedom to slaves, was also extremely common. Rarely was a slave actually a slave for life in ancient Rome. Slaves in Rome even had a few very limited legal protections. They could, with permission of the master, live outside of the home. They were also protected from the most extreme abuse, although beatings “with an empty hand” were allowed (in other words, they couldn’t be struck with an object). Obviously, abuse still occurred frequently, and Roman slavery was still a very cruel and terrible institution. However, most people considered slavery as a temporary condition, something more akin to a jail sentence with hard labor, than a permanent state of life.
Now, when the Roman Empire collapsed, there began to be new rules for the enslavement of people. First, slavery didn’t happen very often between 500-1400 AD, but when it did, Christians were no longer permitted to be enslaved. Only infidels, or those that had learned about Christianity and rejected it, were permitted to be enslaved, since it was believed they were doomed to hell anyway. By 700 AD, this primarily applied to Muslims, although a few black sub-Saharan Africans were enslaved as well.
So, what we have prior to 1400 is an institution that was seen as a temporary punishment that was regulated and was not based on race. It was seen as morally wrong, but was far more morally ambiguous than it would become.
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