How about Assassin's Creed, Mongolian Empire. You could work for Genghis Kahn, and spread fear through Russia, China, and really the rest of Eurasia. The game's story would have a little less depth, and moral ambiguity than what might be expected of AC, but hell. Brutal Murders used to cause cities to surrender without a fight would be a lot of fun. Any of the Brutal Empires could do this, Assyria, the Huns. Even Babylon to some degree.