Dark Compliance was the brutal doctrine of conquest adopted by the traitor Legions during the Horus Heresy, a savage inversion of the Imperial Compliance that had brought worlds into the Emperor's fold during the Great Crusade. Where the old way sought to enlighten and integrate a defeated population, Dark Compliance sought only to terrorise, enslave and break them utterly.
Worlds subjected to this new order were forced to renounce the Imperial Truth and swear allegiance to Horus, their leaders slaughtered, their populations decimated and their spirits ground down through calculated atrocity. Fear, not loyalty, was the currency of the Warmaster's growing dominion.
The Word Bearers and Night Lords proved especially adept at this grim work, wielding massacre and terror as instruments of statecraft, binding whole systems to the traitor cause through dread of what defiance would surely bring.