Meanwhile, aeons passed and the Necrons slept on, their machine slaves and constructs guarding them while they slept on Tomb Worlds that had been purged of all life to keep the Enslavers from their door. This plan worked with an amazing degree of success until the Necrons were awakened by the forces of the Imperium of Man in the 41st Millennium to plague the galaxy once more. They discovered a new and unexpected age of interstellar civilisation and war much like the one they had left behind 60 million standard years before.
The galaxy is blossoming with life once more but is still overrun with latent psykers and worshippers of the infernal Chaos Warp energies first unleashed during the War in Heaven. It will take time and a great many machinations for the Necron dynasties to regain their rightful place as the rulers of the galaxy; the agents of Chaos must be overthrown; the dangerous Aeldari, inheritors of the Old Ones' mantle, eliminated; Humanity subjugated and the great work cutting off the material universe from the Warp completed before a new age of Necron dominion can truly begin.
But the Necrons are ageless and undying, their technology still unmatched by any of the younger starfaring species. And time is always on their side...