Necrons (since they will be next) are a race of machines run by the souls of an ancient race known as the Necronytar. The Necronytar witnessed the birth of a star god inside their own sun, and they allied with these StarGods, who gave the Necronytar technology for new, immortal bodies, and they became the Necrons. The Star Gods waged a war with a race of hyper-powerful beings known as the Old Ones, who responded by creating the Eldar to fight for them, and the Krork (who later became the Orks). The Eldar, alongside their god Khaine and with the help of wraithbone warriors forged by another Eldar god (forget who) they defeated the Necrons and imprisoned them in Tomb worlds. Khaine was shattered, and his fragments became the cores of craftworlds that spawn Avatars. The Eldar went on to form their empire, but they became far too emotional, and their psychic power grew immense, and this resulted in the birth of the Chaos god Slannesh, killing billions of Eldar, and forming the Eye of Chaos. Only four groups of Eldar survived; The Craftworld Eldar, who were far enough away to survive and formed the Aspect paths to keep themselves safe from Slannesh, the Exodites, who had seen the danger and reverted to an Amish/Mormon-like existince, the Eldar Harlequins, a group of mysterious warriors who have access to the Black Library (a store of Immense Warp power) and travel the warp fighting Chaos, Star Gods and the like, and finally the Dark Eldar, who embraced their tradgety, hoping that by pleasing Slannesh he won't feast on their souls. Anyway, the Necrons after thousands of years have begun to awake and attack the galaxy, with the help of the Star gods. They attack in massive Monoliths, from which powerful Necron warriors spew forth thanks to a portal in the middle of it. The Necron adgenda is unkown, but it may be to awake the two known sleeping Star Gods; the Dragon, said to be the machine god of the Adaptus Mechanicus, who is known to be buried on Mars (Crappers fr the Imperium) and another, even more powerful one, who is said to be trapped in a massive Dyson Sphere on the edge of the galaxy.