In the vast expanse of the void, there was once a young and hopeful world named Algine. The same planet still exists, orbiting the same sun on the same path with astronomical alterations over the same billion year cycles. The name of the planet, and the life thereon, have changed irreversibly, but the ancient world cares little for the lives and thoughts of men.
This world could be thought of as a good place to live, when taken against the nightmarish homes of most imperial citizens, and in many ways it is. After the planet was cut off from others via the Warpstorms of the age of strife, it's colony fell back towards an older age like many others, but unlike those the people of Algine slowly began to ascend again. They marched past the chaos of the dark ages in a golden age of technology, fuelled by the echos of faded memories and the desire for a better future. Over time, by luck and little else, the planet's population of psykers were reduced to legends, ultimately shielding the world from the eyes of chaos.
But no luck can last eternal. As the people of Algine slowly reached out into the stars, the stars clawed at them and an unseen rot began to spread. One day, which by the records of the imperium would be listed as 9 200 895.M4, the planet was struck by six objects from beyond its solar system. On investigation, no debris were found, but eight members of the search team were found unconscious with no memory of their attacker. Twelve others were found dead.
The alien threat had arrived, invisible and hungry.
More obviously, in 9 637 934.M41, the planet was discovered by the imperium. A mighty battleship burst out of the warp a mere few hundred miles from the planet. This soon lead to war.
The unseen aliens, the imperial army and the planet's population itself. Each was staring solely at the others. Non noticed the fourth faction.
Another imperial battleship sailed into the solar system. It's speed had been reduced by the asteroid field it had travelled through, the hundreds of impacts ravaging the ship's hull and robbing it off energy. But not once, not one time in over eleven thousand years, did the dead ship truly stop.