There were undead before both the Lich King and Arthas. Necrolytes would raise skeletons, and Gul'dan created the Death Knights. Necromancy in WoW is a fel oriented magic, passed on to mortals by demons - in one way or the other.
---------- Post added 2012-05-26 at 04:13 PM ----------
Have you actually ever read Lovecraft?
---------- Post added 2012-05-26 at 04:14 PM ----------
Ner'zhul was banished shortly before Wotlk.