Oh no, he's not biased...
(1) Was the Civil War an exercise in nation-state formation? Most dispassionate commentators would say that along with the War of Independence, it was one of the two most essential events in forming the US nation state.
(2) Was the Civil War an exercise in white supremacy?
I don't have a problem with bias. Most are going to have bias on these issues.
What is a problem is that his bias overwhelms his ability to think and draw conclusions in a scholarly manner. I would question his ability to discuss viewpoints that run counter to his. To him, education is perhaps considered indoctrinating his students with his viewpoints instead of offering a multitude of viewpoints and helping students to develop the critical analysis skills in analyzing the viewpoints.
In other words, it's his way or the highway in his classroom. And that's not being a good educator - it's being a propagandist.