In 1311 Avard, a necromancer by the name of Demik Coruth-Liss discovered the secret hiding place of the Book of the Dead. The artifact supposedly was the book that the God of the Dead used to inscribe the names of the dead and dying. The God of the Dead literally quit during the Storm Wars, turning over his powers and portfolios to the Scavenger God and going into a self-imposed exile. The Scavenger God had the artifact hidden within a distant mountain, and set the avatars of several lost gods over it, to guard it.
A powerful necromancer in his own right, Demik rebuked the avatars, and secured the Book of the Dead for himself. As he began to unlock its secrets, he began raising more and more powerful undead, as well as gathering a small army of aides and followers. Striking a deal with the pirate prince Captain Gale Hoffin, he attempted to raid the Cache Vault of K'Tath on Krikta Island. (For details on the Cache Vaults, read up on the Inquisition and the Avard Accords.) A priest of Galgiran and several friends from the land that would one day be Rakore thwarted Captain Hoffin, but Demik himself eluded them.
The necromancer next turned up on Chirin Island, south of Al Fahim. A brief but viscious fight with Demik's guards ensued, and the necromancer was denied the Cache Vault of Elinthar. A hunting campaign began in earnest, spurred by on by the newly forming nation of Rakore. A strike force known as Firestorm raced to reach each vault, sometimes ahead of Demik Coruth, and sometimes behind him. Several of the Vaults were destroyed by their own protective measures, rigged by Demik's mages to detonate when anyone followed them.
As Demik Coruth-Liss gained access to more and more Vaults, his power increased, and his undead minions eventually grew powerful enough to raise more undead. The Chosen of many gods were at a loss to explain the weakening of their power, and the weakening of the Relics of their faith. Essentially, Demik was draining the Relics with the Book of the Dead, drawing on the souls stored within those Relics to forcibly animate more and more of their corpses.
In the middle of this chaos, the Fourth Crusaders invaded Kur Maeth in 1318 -- after Nabrolians had invaded the ancient city-state. The plethora of bodies in the aftermath of two invasions proved an irresistable target for Demik, and Kur Maeth fueled a small army of undead. The undead did not stay to battle the paladins of the Fourth Crusades, but instead departed in the stealth of night, crossing the mighty Dreneb River, and moving eastward into the Laekenala Jungles.
Between the end of 1318 and the beginning of 1319, the Granite Mountains sank, and the Sea of Kiriath formed. Millions of dwarves died, and several other nations were no more. This, too, fueled the necromancer's power, and the Sea of Kiriath became a seething cauldron of undead, ghost ships, lich-krakens, and worse.
Firestorm eventually realized that the marching armies of undead were merely distractions. Scattered across all of Gaeleth are large Towers -- indestructable, and infinitely old. Both Firestorm and Demik's people figured out how to use the Towers to teleport vast distances, but they had another purpose. They were slowly cycling up to something, and the priest of Galgiran that led Firestorm finally figured out what was going on.
For five hundred years -- since the end of the Storm Wars -- a spell had been building power. The Towers were the focal points of the spell, and they would work to teleport the whole of Gaeleth to some other place. Some argue that the spell, five centuries in the making, was the reason the prophets spoke in One Voice to silence the mages for half a millennium. A spell that powerful could be affected by, and would affect, other spells because of the sheer power of it. Unfortunately, Demik Coruth-Liss sought to tap into that power, and rather than teleport the entire world, use that awesome energy to raise the Dark God as his personal servant: A god in the service of a mortal necromancer.
Unfortunately, Firestorm failed. Demik acquired enough power and knowledge from the Vaults to locate an ancient, secret temple to Nathel that had been deep in Karatikan Territory. With his undead hordes assaulting the world, no one paid attention to Galth Island, north of the Sea of Kiriath. There, in the Voman Mountains, the necromancer succeeded in raising the Dark God.
Gaeleth was plunged into darkness.
Battling through the most elite of Demik's undead guard, came the Chosen of Garalus, riding a titanium dragon, and backed by a formidable strike force. Eighty-foot clones battled dracoliches, while uncountable death knights and dread knights fought against the fearsome combat power of one of the last ArchMages, armed with a sphere of anhilation that responded to his will. As Nathel slowly regained consciousness, his first and last thought upon his ressurection was interrupted as the God Slayer plunged through his avatar's formed, destroying him in a concussive outburst of energy that equalled that of his first death.
The resultant energy discharge recycled the Towers, and instantly teleported Gaeleth... 'somewhere else'. The world found itself orbitting a massive gas giant known as Maroth, as all of the undead powered by the Book of the Dead were slowly sucked up into the Towers massive stores.
Demik himself was turned to stone on Galth Island, his stone heart finally overcoming him. A large monastery has sprung up around the site of the ancient temple to Nathel, and around the statue of Demik, to guard it, study it, and if necessary, destroy it.
In the aftermath of all this chaos, the Inquisition found itself undermined considerably. Even the stars were different. The world literally was somewhere else, and the gods were silent on why, and really even how. Few know the secret of the Towers -- Demik's people are dead or scattered, and Firestorm is keeping that secret for the Rakoran government.
Not all of the undead were destroyed. Some were powerful enough to resist the Book of the Dead. Rather than raise the ire of the Inquisition, many lie low, biding their time, but less intelligent undead wander about, seeking either a master to lead them, or merely as lost in undeath, as they were in death.
The priests of Curiss, the current God of the Dead, seek out and absorb as many of the undead as they can. The priests of Arpelos seek to destroy the undead that remain. The soldiers and paladins of Yatindar hope to end the undead menace through any means necessary.
The events of of the War of the Undead have unsettled the lands, and changed the nature of history. Questions are being asked, and the answers aren't pretty.