The Necroquake

Nagash's grave-sand pyramids invert Shyish and loose a tide of ghosts on every realm.

The Necroquake was a vast explosion of death magic centred on Shyish that raised hordes of the undead across all the Mortal Realms - Nagash's doing, and the first stage of his plan to spread the power of Death over all creation. The realmstone of Shyish gathers at the realm's edge, and for centuries Nagash's servants hauled this grave-sand to Nagashizzar, where he fused it under the heat of his magic into glassy black monoliths and towering pyramids; Sigmar and the gods of Order took it for vanity and understood too late.

The structures inverted Shyish's magical polarity, drawing the realm's power to its heart and dragging its underworlds toward Nagash's capital to be ground into pure death magic, and the collapse hurled a wave of undeath through the aether into the other realms. Every dead soul was drawn down the silver cord to its remains and rose as a Nighthaunt gheist. In one act Nagash laid claim to every realm, and Order, Chaos and the greenskin tribes alike fell back before the hurricane of undeath.