It is unlikely that the hostile and destructive creatures that live below the surface of the world would have ever joined into a single force without a single defining event: the arrival of Hex. The Hexing Gems were scattered throughout the world, and the first necrotic were awakened.
The necrotic are infused with an alien intelligence that gives them tremendous powers of persuasion. They managed to forge mutually beneficial relationships with hostile races that had no sense of what an ally was. The cruel vennen, the destructive dwarves, and the hyper-aggressive shin’hare all agreed to align with the necrotic.
Three hundred years ago, the necrotic officially formed the Underworld alliance, and soon after, the Underworld Incursion was launched. Though the conflict now stands at a stalemate, ongoing altercations with their Ardent enemies constantly threaten to once again erupt into a full global war.