Chaos Cult - Horus Heresy: When the Age of Darkness inaugurated by the Horus Heresy descended upon the Imperium of Man, the galaxy reeled in shock that the Emperor's greatest champions -- the primarchs and their Astartes sons -- would seek to tear down all they had built during the Great Crusade. The Legiones Astartes were created to be the very best of Mankind, the champions and protectors of an entire species, the stalwart defenders against the unnameable horrors that had brought humanity to the brink of destruction during the bleak millennia of Old Night.If near-demigods such as Horus, Fulgrim or Lorgar could be corrupted under the baleful influence of the powers of the Warp, then what hope remained that the teeming populations of mortal Humanity would do otherwise?As the Horus Heresy entered its second year and the fires of war swept across the Imperium, the true and horrific extent of the Traitors' sins were exposed. The earliest battles had revealed the Warmaster Horus to have turned numerous august bodies to his cause, including those within the Mechanicum Taghmata and the Legio Titanicus, as well as uncounted Excertus Imperialis Auxilia units.At Calth however, a new element of the Traitors' blasphemy was employed -- vast hosts of mortals sworn to serve the Traitor Legiones Astartes, devoted to them not only in body but in soul; these were deluded "Warp cultists" -- so-named because of their mindless veneration of the creatures that dwell in the Empyrean and of their fallen Legiones Astartes masters.Warp cults had of course been encountered, albeit infrequently, during the progress of the Great Crusade. Such debased examples of Humanity were usually found on worlds within proximity of existing Warp Storm activity or with a prevalence of psyker birth within the general population. Such cults were oft times tainted with interaction with xenos lore or contamination by alien species, or promulgated by some alpha-level rogue psyker with messianic or apocalyptic pretentions.Direct confrontations with such threats were however rare as they were either a relatively minor factor in a larger Imperial Compliance campaign or encountered in highly unusual circumstances, such as the lengthy persecution of the void-born Gethora Warp-Witches by the Night Lords Legion across the Vaomir Reaches in the late 970s.M30.The principal reason for this was that since the very beginning of the Great Crusade, any world encountered with substantial Warp breaches in evidence of the kind that such cults either promulgated or were often spawned from were simply destroyed via Exterminatus from orbit without direct confrontation.This order had been a direct and unwavering dictate issued directly by the Emperor and one that had been upheld almost without exception until the Word Bearers themselves began to covertly subvert and ignore it for their own ends.As to the "truth" of such veneration, it was considered no more than just another false religion, meaningless in the context of the Imperial Truth, and consigned to the darkness from which the Great Crusade was delivering the galaxy, or so it was believed.The truth, however, was that on many fringe and backwater worlds declared Compliant by Horus' supporters, entire populations had not just been allowed to shed the mask of civilisation and reason and surrender themselves to the Warp, but actively encouraged to do so by the work of the Word Bearers and other, far more hidden, forces.As the insanity of galactic civil war gripped the Imperium during the Horus Heresy, previously law-abiding peoples rose up against their masters, slaughtering those in authority in bloody displays of long-repressed hatred.Once-productive workers smashed the machines they had tended for generations and set manufactoria to the torch, whilst amongst the madness educated men and women cast off the secular reason they had been born into and resurrected the heathen idolatries of their ancestors.