The Undead in the Sacred Desert slowly but surely overwhelmed the rest of the Sacred Desert. Hundreds of Lords' territories had already been bulldozed, the hard work worth years, if not decades of their lives destroyed within weeks.
However, the threat of the Undead forces didn't lessen. The Undead forces were strengthened instead. Most higher-ups believed that a Greater Lich was the core issue. He controlled the Souls of the deceased and forced them into submission before putting them back into the bodies of the deceased, resurrecting them as Undead without emotions, or control over their bodies.
It was rather easy to tell that some sort of being with profound necromancy mastery was at work, but nobody found the Greater Lich, or whatever being it was that resurrected the dead.
The only advantage was that only a few Summons and Awakened could be resurrected as Undead. Even better was that their combat prowess was nowhere near their peak.