Talk about the things they didn't teach you in school. I went through the California public school system back in the day when it actually taught you (well, me, anyway) to read and think about things. And I don't recall ever hearing one single mention of this. But let's start with a question it probably never occurred to you to ask. Say you are a slaveholder in the pre-civil war South, and you have more slaves than you want. How do you sell them?
In this article, in the October 2015 Smithsonian Magazine, I found the appalling answer.
Retracing Slavery's Trail of Tears
It's longer than the usual Smithsonian article, but I read all of it. It was horrifying but extremely educational. I recommend we all read it, and remember, so we can not do that ever again.
As I regularly post, if we as a people don't understand who we were, and what we did, how can we possibly avoid doing it again?