Imperial Army - Hammer of the Emperor: When the great Warp Storms that had cut off Terra since the end of the Dark Age of Technology subsided, and the Age of Strife came to an end in the late 30th Millennium, the Emperor of Mankind deemed it time to begin His Great Crusade.This was a massive campaign begun in ca. 800.M30 to conquer the galaxy by which He and His armies would free all Human-settled colony worlds from alien oppression or primitive ignorance and reunite the Human species across the galaxy under the single banner of the new Imperium of Man.The Great Crusade marked a brief era in Human history of rebuilding, reunification and rapid technological advancement following the complete regression of Mankind into techno-barbarism during the 5,000 Terran years of the Age of Strife.The Emperor sought to unite all of Humanity under one banner following the Long Night of the Age of Strife, and end inter-human conflict. Once united, the Emperor intended to begin the next stage of His great plan to ensure Human domination of the Milky Way Galaxy.At the forefront of this time of expansion and reclamation were the mighty Space Marine Legions -- the Legiones Astartes -- the finest warriors Humanity had ever created, each the equal of a dozen normal men. Despite their formidable battle prowess, the forces of the Space Marines were not limitless, and the relentless demands of building a galactic empire pushed the Legions further apart.Separated by countless thousands of light years, their presence became ever more scattered and diluted. No doubt from the very beginning, the Emperor realised that while His Legiones Astartes would be His foremost agents of war and conquest, the sheer scope of the undertaking of the Great Crusade -- no less than the liberation of the entire galaxy -- would require far more manpower, spread over a wider area, than even hundreds of thousands of Space Marines could hope to achieve.They simply could not be everywhere at once, nor would they be best served by undertaking roles ably filled by ordinary Humanity. From this reality the Excertus Imperialis was born; billions of second line and support troops, functionaries, labourers, void crew, logisticians, almoners, adepts and staff officers, and the countless quantities of weapons, equipment and war machines, void conveyances and warships they needed; all to make the Great Crusade a reality.Within this vast body of men and women under arms, organised and formulated by the Emperor's own transhuman intelligence, were many highly specialised divisions, each created to serve a singular purpose, each a vital cog in the vast Imperial war machine.The Emperor required more manpower to ensure the momentum of the Great Crusade did not falter. Each newly conquered or liberated world brought into Imperial Compliance during the course of the Imperial campaign was assessed and a census taken of its population.From this, the Emperor's administrators of the Corps Logisticae, the forerunner of the later Departmento Munitorum, calculated the tithe that each world was to pay in the form of regiments of soldiers and war materiel. The numbers of regiments raised from each world varied enormously in accordance with the size of each individual planet's population.Sparsely populated worlds would be tithed to supply only a handful of regiments annually, whilst the overcrowded Hive Worlds near to the Galactic Core would have to supply hundreds of regiments every standard year. This huge body of soldiers soon became known as the Imperialis Auxilia, or more commonly referred to as the "Imperial Army".Although the Imperial Army was not as powerful as the Space Marine Legions under the primarchs' command, the Imperial Army regiments were nevertheless useful additions to a primarch's fighting strength. A Space Marine Legion often had hundreds of auxiliary Imperial Army regiments fighting under its command.These troops were used to reinforce the Space Marines and were frequently deployed in sieges, mass invasions and to garrison newly-conquered worlds. The Imperial Army was rarely deployed within the home system of the regiments that comprised it.In fact, this was actively avoided by the primarchs in command of these regiments to ensure that the soldiers' loyalties lay first and foremost with the individual primarch and the Space Marine Legion to which they had been attached, and alongside which they fought.