"After nearly a thousand years, the Warp Storms that have isolated the Corvus sub-sector from the rest of the Imperium have begun to abate. Once a rich and prosperous sub-sector sitting at the nexus of military and economic power in the galactic region, who knows what changes a thousand years of isolation will have wreaked on the sector? Chaos and ruin might reign, or some vestige of Imperial governance may yet remain, as might arcane technology thought lost to the Warp."
The tides of the Warp are fickle. One day the storms engulf a huge swath of space, a thousand years later they vomit it back into reality. The Corvus sub-sector had finally returned, and it brought something with it. Centuries in the Empyrean had tainted the sub-sector, leaving not one planet free from the touch of Chaos. Bustling Hive Cities reduced to charnel houses, gargantuan Manufactorii filled with smoke and wreckage, ancient Space Stations quietly rotting save for the echoes of the dead, such was the state of the Corvus sub-sector upon its reentry into real space.
Despite the desolation, Corvus was a strategic lynchpin in the Imperium's continued survival. The Crusade of Light was quickly assembled to reclaim and purify the sub-sector. At the tip of the spear were elements of the Ultramarines, Crimson Fists, Iron Hands and Space Wolves. They launched early, taking the fight to the enemy and paving the way for the more ponderous elements of the Crusade.
The ruins of Corvus were not abandoned. Chaos had taken root in every planet and awaited new blood to drink. The capitol planet, Corvus Majoris, was once a teeming Hive World. What emerged was a desiccated plague husk. Typhus, the Herald of Nurgle himself, had spread his contagion to the entire planet and looked to claim the system in Nurgle's name.
The Death World Alfrost had survived the millennium with much intact. However, as a barren, ice-covered rock, an Alfrost barely surviving was not much different from Alfrost at the height of Imperial control. On this frozen wasteland, a band of Dark Eldar led by the Wet Knife Haemonculus coven set up their diabolical workshop in the remains of an Imperial command bunker. A thousand years in the Immaterium was nothing to the torments meted out by the Haemonculi.
As the Warp spewed out the planets Corvus Majoris and Alfrost something else came along. A massive conglomeration of interstellar flotsam, a Space Hulk, emerged in orbit of the Forge Wold Junkatta. The Hulk was far from abandoned, for within minutes of arrival massive chunks of rock and metal launched towards Junkatta. Junkatta's masters had long since abandoned the tenets of the Omnissiah, turning to the Dark Gods to keep the forges churning out demonic machines. Mighty as their chaotic war engines were, they were swiftly overwhelmed and driven off by the Green Tide. Big Mek Gubsnagga and his Dreadmob, "Da Urfshakaz" claimed Junkatta and its Mantufactorii to produce more and larger smoke-belching monstrosities.
Initial landings by the Crusade of Light were disastrous. Erik Morkai of the Space Wolves, Master of Runes and overall commander, was ground to paste under the Deff Rolla of Gubsnagga's personal Battlewagon "Da Skwisha". Varro Tigurious barely escaped a Dark Eldar ambush even his powers of foresight could not detect. Iron Father S'mahs Erckuf, however, led his warriors to establish a beachhead on Corvus Majoris with the help of his Cadre of Ancients, half a dozen Ironclad Dreadnoughts.
Gubsnagga quickly went to work adding the remains of the Space Wolves to his infamous "pit uv gubbinz". As he worked he was contacted by a vision of Typhus. The Herald of Nurgle declare Corvus the dominion of Nurgle and any Imperials were to be surrendered for sacrifice. He promised no harm to the Orks if they complied, provided they limit their ambition to Junkatta alone.
"Ya spiky boyz gotz more stinkz den brainz. Deze beakies I krumped belongs ta me. Dis rock belongs ta me. Dat rock belongs ta me. ALL DA ROCKS BELONG TA ME! I'z gonna stomp all deze humies first, den I'm setting me Kanz on yer stinkin spiky boyz."
Gubsnagga set to constructing the first of many Stompaz, the personification of Orky belligerence. Typhus consolidated his position, plotting his revenge on both the Imperials and Orks. The Dark Eldar observed this in between their "experiments" and decided to let the brutes sort things out between themselves. Imperial forces regrouped and prepared for the next offensive, attempting to take advantage of their divided foes. Meanwhile, the Warp continued to churn and more planets began to emerge.