The History Channel, I've been told from people who object to most of its programming, tends to glorify war, conflict, conquest, and when it comes to American history, generally tow the conservative line. I have some problems with this as well because some of the programming sounds and feels like a government sanctioned text book.
The left as a rule, dislikes war, thinks war doesn't solve anything (even if it actually can), and is suspicious of patriotism, because they think there's too much of it. So that pretty much makes all the programming of the history channel, which focuses primarily on human conflict, right-wing programming to brainwash the public in their eyes. A left learning history channel would run endless documentaries about unions fighting corporations, reruns of Chomsky's stuff, and stuff like the Power of Nightmares, and maybe some documentaries and programming on warfare during the politically correct days of the year when its ok to celebrate war, but only World War II, and only the victory against the evil facist Nazis.