Belligerent, evil demons

One variety of demons, which doesn't have a specific name and are unplayable, have set up a fortress in the Desecrated Lands. They have started to amass a large army, and the other races are worried that they may strike. These demons are formed when humans have experienced prolonged exposure to evil magic and dark forces, and have been corrupted by them. These demons have been known to kidnap people and hold them hostage, thus quickly turning into demons.