Slavery has existed as long as humans have existed. The Christian Bible has many references to slavery. Every race has at some time been enslaved. The Roman Empire was an equal opportunity enslaver, enslaving some members of just about every race they encountered.
In the Americas slavery was not an exclusive trait of North Americans of European descent. In fact the vast majority of Africans transported to the Americas did not go to North America – only about 4% had North America as their destination.
Once Africans arrived in North America and were sold some of them, or their descendants, ended up being the property of free blacks. Native Americans were also prominent slave owners, especially among the Five Civilized Tribes.