I'm not sure which expansion this came with, but it ruins the game imo. A Plague of Savagery makes minor factions 50% stronger until you pacify all the villages in a certain region. The region is never nearby and the AI never clears it on its own. The quest always happens in the early game when you have very few units and they are ill equipped to deal with the insanely stronger MFs. I think a more appropriate boost would be about 20% for the duration of this quest.