Forget what you know of the tragedies of demi-gods and the fall of empires, a different future awaits, brighter but no less dangerous.
The Chaos Gods have succeeded in murdering the nascent Primarchs in their archaeotech cribs, but in doing so have robbed themselves of the pawns and pathways they needed to topple the Emperor’s realm, whilst the lifeless bodies of these infant demi-gods have provided the genetic material necessary to stabilise the geneseed of the fledgling Legions. Whilst each Legion has its own affinities and purposes within the Emperor’s grand plan, there is now no longer any place for dark secrets or deficiencies to abide and find purchase.
Pushing out into the universe without the Primarchs, the Emperor’s Great Crusade has nonetheless achieved most of its aims, albeit it harder fought and often at greater cost. Its true aim, the propagation of the Imperial Truth, has robbed the Chaos Gods of the belief that sustained them, too heavily invested in humanity to seek out worthy successors in a galaxy of dwindling potential as the Legions extinguish race after race of inhuman aggressors.
However, the galaxy is not without threats; seeing their greatest foe all but vanquished, the jubilation of the arcane alien puppet masters known as the Cabal has quickly turned to horror as the Emperor turns his attention to ensuring humanity’s ascendance as sole inheritor of a secular Galaxy.