The area of the galaxy of Archeras has long been a dark and perhaps dangerous place. After the Gods abandoned the mortal realm, it fell to the citizens of the world of Exarch to organize society, and they did so quickly. At the center of this civilizing movement was the Core, an area of space closest to the Veile Nebula, an area of anomalies unexplainable by conventional science. From the Veile, energies 's powers in ways that broke the normal laws of physics.
In an amazingly short period of time, the races of Exarch spread out across Archeras. Contact was made with other races, including many who had once graced the pages of myth and legend. Colonies were established, nations rose in a relatively peaceful existence. Even the occasional strikes of demonic forces from dimensional rips barely fazed the galaxy. Life was going well.
Then a period of ambitious uncertainty came over the capital worlds of the Core. The inhabitants fell into debauchery and abandon. Blinded by greed and isolationist sympathies, they shut out the worlds beyond their insulated little area. Soon all communication between the Core and the outers worlds failed. No news came, whether via ship or via pulse communication.
None but for one tiny group, a moderately large armada of anything which could cross the stars. Members of the frontier world of Solwe received the drifting hulks of steel, gently guiding them into orbit. No messages came from their bridges. Nothing at all. The inhabitants sent a small expedition-to find a charnel house of rotting flesh;rotting flesh which attacked them with sudden and unholy fury. Only in perhaps ten to twenty vessels did they find anyone alive, perhaps two million refugees crammed inside of varying race. All had the haggard look of survivors of a great cataclysm.
Those few survivors formed the Alliance. The Core worlds had fallen prey to a sudden and completely annihilating strike. The center of galactic culture, Exarch, had fallen in days. With it's resources, the threat, known only as the Shadow, had taken Core world after Core world until nothing was left but planets of the dead. The Shadow was moving, and they were, as far as they knew, the only living survivors of an area formerly with a population of several trillion people.
Few responded to their cause. Few cared. Most were too busy fighting off their own problems to worry about a crusade to a hazardous and perhaps stripped area of the galaxy for almost certain defeat. They didn't have to go to the Shadow, soon enough, though. The Shadow came to them.
This is for the history of the Shadow-alliance/palsan war history.