Imperialis Militia - Imperium Split Asunder: With the coming of the Horus Heresy, the Imperialis Militia was as split in its loyalties as was every other division of the Imperium's armed forces. When the Warmaster Horus' betrayal was revealed, so too was that of countless planetary commanders, forcing those not sharing their master's conspiracy to choose whether to follow or oppose them.Many militias were brutally purged in the opening solar months of the Horus Heresy and officers who could not be trusted to follow orders were replaced, while on many worlds where loyalty was divided, open civil war erupted, internecine strife that would in some places last out the length of the Horus Heresy and into the years of the Scouring until it was resolved.Nor was this phenomenon limited to Traitor worlds, for the betrayal was greeted with such shock that a wavefront of paranoia spread out across the Imperium, unevenly, as world after world was gripped by the horror of what had occurred at Isstvan III, or some more local outbreak of open conflict was revealed to the population, who feared it might be visited upon them too.As battle lines were drawn and allegiances determined, the Imperium's worlds looked to raise more armies, either to defend themselves from the oncoming hosts of the Warmaster or to take up arms alongside them. Initially, entire planetary defence militias were swept up on both sides in unprecedented numbers, both in the Warmaster's campaign of Dark Compliance, and in Rogal Dorn and Malcador the Sigillite's desperate response to the imminent threat of the invasion of the Sol System.In the forces of the Traitors, many militia regiments soon discovered that they were ranked the lowest of all the Warmaster's servants, and the lives of billions were callously spent as disposable cannon fodder. Only the most ambitious and determined warriors survived such battles and soon the Traitor armies were served by a host of bloodthirsty helot-soldiers, who in many cases worshipped their Legiones Astartes masters as demi-gods.Others were infected en masse with Warp-worshipping cult beliefs by their masters, particularly where the Word Bearers were concerned, succumbing irrevocably to mutation and insanity.The Loyalists too were soon mobilising the Imperialis Militia to oppose the Warmaster's betrayal, in particular across those sectors along the route Horus would take from the Isstvan System to Terra.Entire worlds were often stripped of their defence forces, multitudinous hosts of ill-prepared but determined citizen-soldiers fed into the inexorable grinder of war so that the Warmaster's advance might be slowed as Terra prepared for the inevitable final confrontation.Throughout the so-called "Age of Darkness" that defined the Heresy, mortal warriors from countless worlds fought in the shadow of the mighty Legiones Astartes, often unseen, invariably unheralded. The actions of the Loyalist Imperialis Militia were rarely recorded or celebrated, while those of the Traitors must remain unspoken.Though the Horus Heresy was undoubtedly a war of brother against brother, the war was fought for mastery of the entire Human race, and no people and no world would survive it untouched.