Imperial Army - From the Ashes: After Horus was defeated and his armies had taken flight from Terra into the Eye of Terror, the Imperium was in chaos, weakened and shattered after long years of war. Even though the need for the Imperial Army was as great as ever, those Loyalist leaders that remained, led by the Ultramarines Legion's Primarch Roboute Guilliman, were fearful of a repeat of the rebellion which had cost them so dearly.In the aftermath of the Horus Heresy, massive changes were implemented to civil and military administration of the Imperium on Guilliman's orders, a period forever after known as the Imperial Reformation. To prevent the possibility of large-scale rebellion occurring again, the titanic armies of the Imperial forces were divided.The Space Marine Legions were dissolved and split into separate, 1,000 Astartes-strong Chapters. No longer would the superhuman Space Marines serve as the Imperium's frontline military force. That task would fall to the mortals who had once comprised the Imperial Army -- there were far more of them than there were of the surviving Loyalist Space Marines, and more importantly, should they turn Renegade, the damage they could do was far less. The newborn Adeptus Astartes would assume the role of planetary assault forces and elite special operations troops.Thus the Imperial Army as it had been for centuries ceased to exist. The link between the Imperial Fleet, the Armada Imperialis, and the Imperial Army was formally and bureaucratically severed -- never again would Imperial ground commanders be given direct control over interstellar ships or even their own units' air support.From the ashes of the Imperial Army were born the separate armed services of the Imperial Navy and the Astra Militarum. The Imperial Guard was reorganised into smaller units known as regiments, an existing formation from the old organisation structure of the Imperial Army, and centrally-trained political officers known as Commissars were universally introduced to watch out for disloyalty and to keep the Guardsmen and naval crews properly motivated in defence of the Imperium.The inter-dependence of the newly formed Astra Militarum, the most numerous of the Emperor's troops, ensured that should a regiment turn against their oaths of fealty, they would not be able to spread their treachery beyond a single world, and should an Imperial Navy fleet mutiny, they would not have the ability to resupply or deploy ground troops. The Imperium had learned a harsh and painful lesson following the dark days of the Horus Heresy.This was the birth of the Imperial Guard as it exists in the late 41st Millennium. Divided by logistics and separated by the gulfs of space and myriad different planetary cultures, it remains united by a common duty to the God-Emperor and Mankind.Riddled with inefficiency and bureaucracy, it is often slow to respond and resistant to change, but it continues to function despite the rules laid down by the Adeptus Administratum to limit its power and use by untrustworthy commanders.That no one man can know the extent of the Imperial Guard's total strength at any time is part of this protection and part of its power, as in this way it is truly an army of unlimited size and resources which can meet the demands of interstellar warfare but which will only ever answer to the will of the God-Emperor Himself.