I have no problem with those subjects being included as long as you also include that Blacks were also slave holders and native americans also killed each other and took each other's lands.  Just because the white man conquered the continent it doesn't make the history of pre-white invasion any different.  It just means that the white man had better technology and won once they showed up.  And yes, many whites also committed atrocities against the natives.  But guess what, they happened before whites showed up too.  This kind of thing was happening all over the globe.  Japan ruled the orient with an iron fist. They devastated China and Korea.

So teach all of history as long as you don't focus on any one group.