Sure, teach the history of communism. Don't see anything wrong with it. Teaching communism isn't teaching people that they are inherently oppressors or victims. That won't cause a racial divide.
Ruby Bridges? I looked into it and as far as I see, they're trying to cancel that book because there's no "redemption" at the end, so maybe it seems too grim to teach children. I'm not sure. I don't think it should be cancelled though. The truth is the truth. If anything, wait until children are older to show them that book.
That's not to say that every truth should be taught; a book like that fits well into the slavery/segregation topic.
If you start teaching all kinds of truths that otherwise go undiscovered, you eventually black pill everyone. When everyone is black pilled, society crumbles. Teaching people about how good the rich have it, or how good attractive people have it, does nothing but fuel hatred. Nothing good comes from it. Just like teaching people that institutions are racist, that white people are guilty at birth, that black people are owed reparations.. nothing good comes from this. It takes the individual out of the equation and lumps people into categories that they may or may not fit. Not something that belongs in school.