I've just posted a history to the Pernicious Host, the horde of Daemons flooding over the planet Valorax.
Here we hear tell of their background as well as detail on their base of operations, their planetary access and the side effects of their presence on the natural order of things.
You can find it on the Enemies of Valorax page.
Welcome to Conflict Valorax, an open-ended narrative campaign for Warhammer 40,000 set deep within the Ultima Segmentum on the Eastern Fringe of the galaxy and close to the limit of mankind’s domain. The purpose of this campaign narrative is to richly detail the setting and history of the Valorax star system in order to bring a depth and storyline to ongoing games set within the Warhammer 40,000 universe. Games of Warhammer 40,000, Epic, Inquisitor, Aeronautica Imperialis, Space Crusade, Space Hulk and Battlefleet Gothic are all set within this greater context, each conflict adding detail to the ongoing plot.