In the history of Europe, the Middle Ages or medieval period (also spelt mediaeval or mediæval) lasted approximately from 500 AD to 1500
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https://en.wikipedia.org/wiki/Middle_Ages Slavery in medieval Europe was widespread. Europe and North Africa were part of a highly interconnected trade network across the Mediterranean Sea, and this included slave trading. During the medieval period (500–1500), wartime captives were commonly forced into slavery.
About ten percent of England’s population entered in the Domesday Book (1086) were slaves, despite chattel slavery of English Christians being nominally discontinued after the 1066 conquest.
https://en.wikipedia.org/wiki/Slavery_in_medieval_EuropeRebranding "slaves" as "serfs" was a smart move, but a Rose still has thorns when called by other names.
Just because:
The Church prohibited the export of Christian slaves to non-Christian lands, for example in the Council of Koblenz in 922, the Council of London in 1102, and the Council of Armagh in 1171.
doesn't mean that there were no slaves
within Christian lands, it just meant there wasn't a profit to made trading across those borders (for Christian slave merchants) ...
As a result, most Christian slave merchants focused on moving slaves from non-Christian areas to Muslim Spain, North Africa, and the Middle East; and most non-Christian merchants, although not bound by the Church’s rules, focused on Muslim markets as well.
I'm not seeing any support for your "practically no slaves" assertion.
I am reading explicit mention of ongoing Christian slave merchants post Roman Empire .. which goes to my point that aside from rebranding and cross border regulation the post Roman Christians took a long long time to outright ban slavery.