That is an inconvenient TRUTH that people choose to ignore. Slavery has ALWAYS existed ever since there has been a human race. Who do you think built the pyramids in ancient Egypt. Hint - Jewish and Christian Slaves.
The Globalist Leftist liberals have tried to make people think that slavery was invented by the white British Settlers in the original 13 Colonies that became The United States. They have uninformed people thinking that 3 white guys in a row boat crossed to ocean and defeated an entire nation of black people (which means they think very lowly of the people of that continent) and then brought those people back as slaves.
The truth is that black people conquered other black people and sold them as slaves to people of ALL RACES. And Yes the "Native American" tribes warred against each other for land and took the people who were not slaughtered of the conquered nations as slaves. The Commanche People only took female slaves as they murdered EVERY male, even newborn babies, of the nation they were warring against.
The truth is that black and dark skinned people STILL kill and enslave other black and dark skinned people and sell them into slavery right to this very day.
Another Truth is that WHITE AMERICANS are the ONLY PEOPLE in history to have ever engaged in warfare to end slavery.
The truth is that the globalist left does not want people to know these truths, or to even talk about these truths, because if people knew and actively talked about THE TRUTH the globalist left could not use THEIR LIES to create hatred among people for people of other races making all of humanity easier to enslave.