JJMt said:
Sapper, it's my impression that slavery was fairly common in ancient (pre-Roman) Europe. But as Christianity spread in Europe during the Roman era and following, the Christianized areas eventually abandoned slavery. It wasn't until the much later colonial era and the need for cheap labor in the brutal conditions of the sugar plantations that slavery reared its ugly head among Europeans again.
Is that broadly correct?
It depends on the region and how you define slavery. Slavery was common for criminals and common in the early Middle Ages. The big change was a push by Christian leaders to make slavery immoral when the slave was another Christian. Slavery existed in Byzantium, the Crusader states, and Medieval Spain, where the slaves were non-Christians.
Feudalism, particularly in places like France with the manorial system, had aspects of slavery, though the serfs were not outright chattel property.
This issue of Christianity and slavery loomed large in the early 17th Century as the European states started using African and Indian slaves. Colonies very quickly passed laws declaring that even if Indians or Africans converted to Christianity, that would not change the legal condition of their person.