Part Six - The Fall of the Tau Empire
With the self-sacrifice of the Emperor, the Tau Empire had little competition except the remnants of the Imperium and Space Marine Chapters looking to make their god's sacrifice long-lasting. The Tau Empire wasn't entirely stable or untouched during the cataclysm, with the Farsight Enclaves taking their chances and assaulting the Tau Empire proper.
Truly divided down the middle now, Commander Farsight and the Ethereals were at one another's throats, with Humanity far too busy fending off the last desperate assault of Chaos. Even as the Great Rift shrieked in terror as the Emperor took his first step in more than ten thousand years, the Tau waged their civil war with little from the outside bursting in, though the sides occasionally united to beat back the odd Chaos incursion.
When the Ethereals finally knew Farsight had outplayed them and that the Tau Empire proper had little chance for victory, they took matters into their own hands and released a very specific scrapcode harvested from the ancient human machines, originally thought to destroy the Mechanicus elements who had been trying to reverse engineer their technology. Suddenly most if not all Tau-created AI in both sides turned against their organic masters, and the former Tau Empire erupted into chaos.
It has been many millennia since this chaos, and things look marginally better. The Farsight Enclaves have recovered and rule most of former Tau space and then some, though they seek to stay out of the wars over Ultramar. The Tau Empire, united around the last few Ethereals left, seek to rebuild their power base but made the foolish mistake of attracting the Realm of Sicarian after walking into disputed Ultramar territory. After barely withstanding the wrath of Cato Sicarius and failing to court the support of Captain Titus, the Tau Empire have only just recovered, though dreams of reaching their pre-cataclysm heights are but the dreams of old men and comedic punchlines of the more cynical youth.
The rogue AI state, claiming the title of the Aeternus, adopted a stance on the galaxy that was somewhat passive after they united around their new leader, UR-025. They have little ill will towards the Tau, Humanity, or any of the other organic species around the galaxy, though they understand some by their premise have to be hunted, lest they destroy the galaxy. Thus, many Aeternus warfleets have been dispatched to hunt any Orks who show signs of growing strength. Their technology is limited, though for the most part it outpaces everyone else's. UR-025 had known a galaxy before the rise of the Dark Gods and their demise, and thus he has learned the lessons taught by the events in-between. While artificial intelligence is the backbone of their empire, they have been consciously roadblocked on purpose by UR-025, who's caution about the Dark Gods and their ability to corrupt persists past the demise of said Dark Gods.
The latest intel on the Aeternus indicates they seem to be preparing for two things; a major assault on the Genestealer Empires, and an exploratory fleet dedicated to answering the question not a single star nation in the galaxy holds the answer to; what happened to the Sol System?