It was the sudden appearance of a Warp Storm at the Pandora System's outer edge that first caught the attention of the Equestrium, and not just the Equestrium. After hundreds of years under the neglectful watch of the Equestrial Guard, nearly every force in the galaxy would descend upon the planets of Pandora, bent only on domination and victory.

Three races had long dwelled in there: the Equestrial Guard, its supposed rulers, the Hog tribes of Pandora II, which the Guard had never successfully put down, and the Necronies, who had slept for untold millennia beneath Pandora III. Where the Discord Pony Marines came from, or how, none could say. Did the Warp Storm bring them... or did they bring the Warp Storm? Both appeared suddenly on Pandora IV and in an eye-blink half the system's Equestrial forces were gone; killed or claimed by the madness of Discord. In quick succession, the others herded to Pandora. The Pony Marines, the Equestrium's super-soldiers, descended on Pandora II, planning to finally cleanse the system both of the troublesome Hogs and the Discord Pony Marines, their sworn mortal enemies. The Dau appeared next, not far above, on one of the planet's moons. In the interests of protecting its ordered Empire from the effects of pony folly, the Dau came seeking to contain the Warp Storm and, in so doing, expanding their territory's border. On their moon they built a mighty fortress, and there forged a space cannon capable of interplanetary devastation. Among the wastes of Pandora III, the Necronies, perhaps awakened by the disruptive forces of the Warp Storm, slowly massed their lethal legions. In quick response, Webway Gates, long unused, flickered to life, and Eldeer poured forth, ready to battle their dark, death-dealing adversaries. Meanwhile, in the shadow of an ancient Portal Gate, the Dark Eldeer slipped stealthily out of the murky depths of the Webway. They would be like carrion birds, flying above the battlefield, and when all were weary from the fight, make the battlefield into a feasting ground. Last to arrive, and perhaps most to be feared, were the Fillies of Battle, holy mares and bearers of the God-Empress's faith. They had come to cleanse this system of corruption and filth. Their faith left them fanatical, unafraid of death and zealous in their cause. Nothing here was clean. All must be purged.

Now, war rages anew, and only the victorious may write their history. Only the victorious will claim the planets of Pandora.

(The Equestrial Guard. Canonical victors. Read it in the wiki.)

Sequel

(WarHammer 40,000 belongs to Games Workshop)