The Era Indomitus is the present darkness, the age that dawned when the galaxy was torn asunder and hope returned to mankind in the same terrible hour. With the fall of Cadia, the warp-storm known as the Great Rift split the heavens from end to end, cleaving the Imperium in two and casting half its worlds into a maddening night beyond the Emperor's light.
Yet from that same catastrophe came salvation of a kind. The primarch Roboute Guilliman, last loyal son of the Emperor, was woken from ten thousand years of stasis to take command of a realm on the brink of annihilation. He brought with him the Space Marines reborn as the Primaris, warriors forged larger and stronger than any before, marching to war in numbers not seen since the Great Crusade.
Guilliman launched the Indomitus Crusade, the greatest military undertaking of the age, driving fleet after fleet into the storm-wracked dark to relieve besieged worlds and cast back the tide. Beside the Imperium's renewed might, old horrors pressed harder than ever, and the Chaos Space Marines poured from the Great Rift in legions swollen with millennia of hatred.
This is the age in which the story now stands, a galaxy sundered and burning, where every victory is bought in oceans of blood and the outcome remains forever in doubt. It is not an age of hope reborn so much as an age of defiance, mankind fighting on against the dying of the light because to yield is to be devoured.