It's useless to try to teach this today. American Liberals are so blinded by their anti-America rhetoric that they do not care that slavery is happening right now in Africa, Asia, and the Middle East. It is happening today. Not 150 years ago in America.
They don't care. And you can't make them care about current day slavery all over the world. Because it doesn't fit their very narrow, White people are evil, America is evil, agenda.
The slavery narrative, the Black History narrative, is all agenda driven. Not only is it not about the truth of slavery, it is actually anti-truth about slavery. Because if you try to bring up Boko Haram for example, they will shut you down and kick you out of the room. They do not want to hear the truth. Truth makes them furious.