So does Africa.
It's not much different than the Americas before Colombus. Yes you had the Incas, Mayans, and Aztecs but aside from those it was all a relatively similar cultural hodgepodge. And least we forget, all the vaunted American Indian cultures of note were subdued handily by a few mean as hell Spainards on horseback with primitive firearms. Ironically, the less advanced but hardier and simply tougher Plains Indians put up a much better fight proportionately.