Ruugat of the Earth was a fairly recent lost city, which made him much more dangerous than his "siblings". The Forbidden Magic that animated his pseudo cores was old and outdated, but much more efficient than Thaymos' or Argantyr's.
Ruugat had been created after the advent of the Guardians, when the undead were already considered Mogar's fourth main race
The Warlock King of Yerzath, one of the few Awakened to ever build his own empire, had been impressed by the feats of the Guardians and sorely disappointed by their apparent lack of care for poor, righteous people like himself.
Keeping an empire running required a lot of time that the Warlock King couldn't spend researching new magic. Border wars threatened his empire from the outside as much as his political opponents did from the inside.
