Do not be fooled by appearances, as human civilization may seem to be past the need for concern over undead threats. However, this is predicated on the ability of human civilization to rapidly eliminate the vast majority of newly born undead.
Even if a Ghost King occasionally grows powerful enough to act independently, they are unable to amass any significant scale.
If suddenly there were tens of millions, or even hundreds of millions of undead appearing and spreading destruction at will, threatening people's lives, then even Shen Hao would find it a thorny problem.
With his current level, even sitting upon the "Emperor's Throne" and wielding the "Emperor's Scepter," he wouldn't be able to wipe out all life on an entire planet instantly.
Therefore, should the undead from other worlds truly traverse interstellar space and pose a threat, it will become a matter of great concern.
