The seer council had predicted the return of the Corvus sector many cycles ago. With a keen eye, they had closely studied the strands of fate, attempting to divine the best path to reclaim what was lost. Artifacts thought once lost, were again within the grasp of the council. The worlds of Beth and Savrap; once crone worlds, abandoned during the fall, then lost, were found again. Their ancient treasures again available to their lost masters. They shall be reclaimed, if not just to keep them from the dirty hands of the mon-kei.
Ulthwe was stretched thin. Too many battlefronts to fight on, and not enough of the dying race to fight them all. The council decided that Bel-ei was to lead the strike force to the Corvus Sub-Sector. The seer's had scried upon his path, and knew this task was his. A small detachment was to be sent. Primarily guardians, few shrines had volunteered for this warhost. The seers had promised to send more once the forces were available, once they had been received from AusPost and painted.
Until then, Bel-ei was instructed to seek out alliances with the younger races. No doubt Ulthwe wasn't the only faction interested in claiming these once lost worlds. The mon-kei would no doubt be present, and easily manipulated to Ulthwe's goals. Bel-ei had also ordained the prescence of the Tau. A young race, still trusting of the Eldar. No doubt they would prove useful. Finally, Bel-ei had been informed the Eldar would be fighting beside the Daemons of Chaos. These would prove to make interesting allies, considering the complete lack of narrative justification.
The Strike Force was prepared, staging within the Webway for the correct time to strike.
I joke, but i'm looking forward to this