Obviously in the Roman Empire slavery was prominent. But then after it fell Europe seemed to let go of slavery for a long time, until the discovery of the new world brought it back in full again. Why didn't they use slaves in the middle ages at all? Or did they, and I just haven't heard of it?
Slavery was fairly common up until the 11th century in England, where after the Norman Conquest William the Conqueror introduced laws banning the trade of slaves outside of England.^1 The chief motivation was an increasing push from the Church to ban the trade of Christian slaves. However the trade in Muslim slaves was not banned.