system
A chat on subreddit /r/NoStupidQuestions
human
An interesting fact is that polish people also were slave owners. 

Slavery in Poland existed on the territory of the Kingdom of Poland during the rule of the Piast dynasty in the Middle Ages.

 It continued to exist in various forms until late in the 14th century when it was supplanted by the institution of serfdom, which has often been considered a form of modified slavery, since people were "part of land"  and was sold with it as cattle.
gpt
There are very few countries that haven't at some point had some form of slavery, and in almost every instance the majority of people were not slave owners.