Hi,
The Blood Ravens are actually in this campaign due to them landing on Kronus in search for the artefacts that were left behind by their forebearers.
The story is:
When the Blood Ravens arrived on Kronus, Brother Captain Davian Thule sent a message to Governor-Militant Lukas Alexander to evacuate all civilians and Imperial Guard personnel as to allow the Blood Ravens to begin their purge of the planet. However, Alexander refused, and now the Blood Ravens must fight the other soldiers of the Imperium. Thule regrets having to kill his fellow brothers-in-arms, but orders are orders - Kronus must be purged.
The Imperial Guard regiment under the leadership of General Lukas Alexander arrived upon the planet, in pursuit of the Eldar Farseer Taldeer, due to her actions during the war on Lorn V. Taldeer, in turn, had arrived upon Kronus to battle the recently emerged Necrons. The Necrons had gone into statis upon Kronus millennia earlier, after their war with the Old Ones.
The Ork Warlord Gorgutz had also made his way to Kronus, following the collapse of his Waaagh! on Lorn V. After the Ork Warboss had "landed" his Rok on the Green Coast, he quickly set about subjugating the Feral Orks on the planet, in an attempt to rebuild his Waaagh!
The Word Bearers (Chaos), under the leadership of the Dark Apostle Eliphas the Inheritor, had come to Kronus in order to avenge their defeat at the hand of the Ultramarines during the Horus Heresy. Opening a Warp Gate in the Deimos Peninsula, they sought to turn the planet into a Daemon World.
The Ethereal Caste, the leaders of the Tau Empire, could not, and would not, allow one of their colonies to fall without puting up a fight. Thus, they sent Aun'El Shi'Ores and Shas'O Kais to the planet to reconquer it in the name of the Greater Good.
So, the once peaceful & quiet colony of Kronus, became one of the most savage battlefields in recent history.
I would like to see a campaign on the Horus Heresy or the Black Crusades, they would be cool, play as the Space Marines (defending) or Chaos (attacking).