I love the History Channel, but they do tend to focus on some regions and periods more than others. Basically the prevalence more or less in this order, goes:
WWII
Post-Colonial America
Classical Rome/Greece
"Biblical Era" (An inordinate amount of time interpreting the old Testament)
Middle Ages
Ancient Egypt
Mesoamerica and other Native America cultures (I think the Mayans stroke their apocalypse boner)
East Asia
Muslim Middle East (Has cropped up more due to incessant Templar and Crusade-era stuff)
As you can see, "educational tv" tend to be America-centric, Euro centric and Abraham-centric. China and Japan pop a lot too, probably because a lot of Western expansion has been about trying to get to China. (And even then, one tends not to focus on East Asian cultures that are not China or Japan) I think it also has a lot to do with the fact that they, yes, History Channel ties a lot into movies. You can see a large amount of this stuff was likely made because of Gladiator, 300, Kingdom of Heaven and The Da Vinci Cde. Which probably means we could see more corners of the world covered if say, Hollywood or a few novelists decided it was fascinating enough. But in short, here are cultures that we simply have no spent enough time paying attention to.
Central Asia: I suppose you could say that it isn't completely forgotten about, as we've seen some good stuff on Russia. But you get the sense that people only care about the region when big-assed historical groups come and take over; The Romans, the Vikings, the Ottomans or the Communists. You don't see much on Magyars or the Golden Horde or Sara, one of the biggest cities of the Medieval world, created by a bunch of plains nomads. This region actually had a lot more important stuff going on than say, England, which spent a rather large part of its pre-Empire days as someone's royal bitch.
Brazil: Excusable on some level that History Channel doesn't do as much stuff on Brazil, since it's, in geopolitical terms, pretty young itself. But still, Brazil's a pretty big deal. It's essentially the second biggest success story in European colonization. It's perhaps the biggest fish in the Southern Hemisphere. It's two thirds the population of the U.S. and one of the largest nations in pure area. And in that area? The rainforest. Oh, we care about the Rainforest, but for some reason, picture it with blue-collar Americans tearing it down for the logging industry. Forget about oil, this is a nation with its finger on the world's oxygen valve. But just as with the case of endangered species, we think of Rainforest problems as far away lands that corrupt CEO's mine for resources so they can brag at their Evil CEO poker games. Not the internal concerns of an industrialized nation with the same ambitions we had/have. Let's just say if Brazil went evil, it would be serious business. In fact, that the nation is merely mildly corrupt, and all we mostly know it as a Supermodel factory, probably doesn't speak well of our talents with foreign relations.
India:
kiran59 would approve, but seriously. I don't think I've seen one special of the subcontinent, which is astounding as it's a civilization that has rivaled China in longevity and size. They may have made one about Ghandi, but even then....I was looking at medieval cities with excess population of 50,000, and you could not throw a rock without hitting an Indian one. (As well as a couple in Sri Lanka) I think all we really know about it Yoga and unironic musicals. One thing popular history tends not to realize is the Indian subcontinent was as large and diverse as Europe, and was actually not "India" until Britain conquered it, so it's even a mistake to think of it as this homogeneous culture. Applying a cultural uniformity to the continent is like calling spaghetti "French Cuisine", or calling someone from Michigan a cowboy. But all we know of it is as something that, if we're lucky, we can distinguish from the Middle East. I would like to see more on a culture that had written literature that pre-dates Western civilization, and had spawned two world religions. We're starting to pay a lot more attention to it, but still, I think we need to show its history is more diverse than "Before tech service and after tech service".
Sub-Sahara Africa: In particular, the Mali Empire and predecessors. I understand the subtropical region is not good for preserving artifacts, but we in the popular consciousness tend to view the continent as Egypt's backyard, where a bunch of happy tribal noble savages were minding their own business until the Europeans took them all on ships, where their history, for better or worse, really began. However, in West Africa, along the Niger river, existed civilizations equal to any others in the medieval world. It's now annoying to see black people in a lot of medieval fantasies, because they're usually decked in some kind of European or Moorish garb, their inclusion a stab at political correctness. The thing is, they don't need to be politically correct. An affluent, thriving culture with almost completely African roots did survive during the Middle Ages, and writers of both historical and fantasy fiction should learn to draw from those instead of giving Africans cultural hand-me-downs. History did a great special on the Sahara which briefly mentioned the Mali Empire, but I'd be great to get more insights on this.