Hes conflating colonization with slavery. A horribly thing to do as they were not similar tragedies.

Actually they were very much intertwined.

Colonization was how slavery was justified, commercialized and gone global, and colonial subjects were treated as an abundant work force for their colonial masters (when they were not hunted for fun, treated as animals, or displayed on "human zoos").

https://www.theguardian.com/commentisfree/2015/sep/08/europe...

But even if I was "conflating" the too, that would at best a mistake in the use of words, not a "horribly" (sic) thing to do. Slavery and/or colonization themselves would be actual examples of horrible things to do.

So do you have the examples of civilizations stopping slavery way before the europeans ?