Just thought I'd throw this out there: the Sliders TV show had as its major recurring villains, the Kromags. They were essentially some kind of offshoot of humanity that was more bestial in appearance, but no less intelligent than us...and then they got their hands on some high-tech and started conquering the multiverse. But they had their setbacks...
The same idea could be behind Orcworld. The Orcs, after finding some kind McGuffin, conquered the world...well, most of it. Island archipelagos, rugged mountains, underground cave systems and the like all present their own nightmares for hunting down people who don't want to be found. ESPECIALLY if they have help from Druids and the like- Awakened animals and trees* make great spies and sentinels.
* check my sig for the link to the campaign ideas thread- I have an entry somewhere in the 40s about Awakened Aspen trees...