Chaos - Great Crusade: The Emperor first directed His forces in pursuit of His lost primarchs, no doubt fearing to allow such god-like beings to stray far from His guidance. The Emperor sought after them with His psychic powers and was drawn across time and space to the places where His genetic offspring could be found.In each place they found the primarchs to be full-grown leaders and warriors within their adoptive culture. The Emperor must have believed His experiment to have been a success, for the lost primarchs proved to have no discernible taint of corruption about them despite their brush with Chaos.There are many Imperial legends of the Emperor meeting one or other of His primarchs for the first time during the Great Crusade. Most speak of a mysterious stranger arriving at the primarch's court and performing one or more impossible deeds -- usually including defeating the primarch himself in combat -- before the revealing His true identity as the Emperor -- the primarch's gene-father. In the legends the awestruck primarch pledges lifelong allegiance to the Emperor and happily joins His entourage immediately. It's certain that such stories are used to mask the ugly truth that several of the lost primarchs had to be physically subdued before they would agree to join the Emperor.The Emperor showed great indulgence to His foundlings. As each primarch was won over to the Imperial cause they were given command over a Legion of Space Marines raised from their own genetic material. With their primarch leading them a Space Marine Legion became utterly unstoppable, a fearless army of transhumans that would conquer or perish no matter the odds.Some felt that the love the Space Marines exhibited toward their primogenitors exceeded even their conditioned loyalty to the Emperor. With the Emperor at its head and the primarchs at His side, the Great Crusade swept all before it. It is likely that no greater armada has ever been seen in the galaxy before or since.The Emperor's forces certainly did not lack opposition, and heavy fighting marked their progress. Wherever the silver ships landed the flames of war followed. The Emperor's followers found many strange and terrible worlds in the void of the galaxy where Humans and aliens coexisted, or Chaos reigned triumphant -- these they purged most mercilessly of all.Alien empires were driven back and defeated by the Great Crusade; enslaved populations of captive Humans were set free. Psykers and mutants were ruthlessly massacred and the followers of the Chaos Gods forced into hiding. Many aliens learned to hate and fear the Imperium during the Great Crusade, and the rabid xenophobia of those times has been attributed to all Humans ever since.In some places coalitions of Human worlds had survived the Age of Strife and many of these attempted to resist the Imperial onslaught from Ancient Terra. Untold billions were killed by the Space Marine Legions and much precious technology was lost when the Emperor's forces resorted to brute force to overwhelm more advanced worlds.The Great Crusade's indiscriminate use of Virus Bombs and Cyclonic Torpedoes obliterated secrets that had been preserved for millennia. Increasingly the Legiones Astartes began to find themselves deployed against Human populations whose only crime was an unwillingness to join the Imperium. The Emperor's message of unification had changed to one of domination, and those that did not submit were branded enemies to be righteously purged. The Great Crusade rolled onward relentlessly, sustained now by its own momentum as it swept outward to the very fringes of the galaxy.In the wake of the crusading forces the future infrastructure of empire moved into place on the conquered worlds; local governments and nobility became subject to the Administratum, the Adeptus Arbites replaced judges and lawmakers, over time even mechanicians and technologists became supplanted by the ancient Mechanicum.Planetary governors took control, providing they met their tithes. Decrees from distant Terra imposed rigorous conformity on wildly divergent peoples and cultures, establishing a pattern of oppression and drudgery that became the norm for life in the Imperium.Despite the warning signs, the majority of Humanity rose to the challenge of rebuilding its ancient heritage in exchange for the promise of a better future. For a time the unity and strength of the Imperium seemed unstoppable, and the Ruinous Powers of Chaos appeared to have retreated to their own realms. It was not so.