ca. 001.M31 Ark Reach Cluster Campaign - The Ark Reach Cluster had been discovered by the Word Bearers Legion's 47th Expeditionary Fleet; it was a group of binary stars occupied by a number of belligerent planetary empires that rejected the Imperium's offer to become part of the Emperor's growing demesne. This Imperial Compliance action of the Great Crusade was carried out through the combined efforts of the Thousand Sons working in concert with elements from the Space Wolves and the Word Bearers Legions. The first four star systems fell to the Word Bearers and Space Wolves. But the fifth and especially the sixth world, known as Shrike, required the assistance of the Thousand Sons. The return to the XV Legion of the dreaded mutational "Flesh-Change" occurred at the conclusion of this campaign and helped to bring on the eternal enmity between the Space Wolves and the Thousand Sons, as the Space Wolves increasingly regarded the Astartes of the XV Legion as "impure" and blasphemous practicioners of psychic sorcery similar to what had destroyed human civilisation during the Age of Strife.
ca. 001.M31 Subjugation of the Akum-Sothos Cluster - The Aukum-Sothos Cluster, which had been brought into Imperial Compliance by the Luna Wolves early in the Great Crusade, had rebelled against Imperial rule due to the actions of controlling xenos. Horus had formulated a plan to cast down the so-called Unsighted Kings, the xenos-possessed leaders of the insurrection, in a lightning war that would purge the afflicted population while retaining the cluster's highly developed infrastructure for future re-population by the Imperium. The Warmaster's plan called for the bulk of four Legions -- the Luna Wolves, Space Wolves, Iron Warriors and Raven Guard -- to converge on the heavily fortified lair of the Unsighted Kings before a final, overwhelming assault was launched. Despite his misgivings, Corax complied, and assigned the majority of the Terran-borne Veterans of the old XIX Legion as the assault's vanguard element. At the height of the battle, with the assault companies decimated and the attack faltering in the face of overwhelming fire, Corax himself led the forlorn hope, his battle cry firing the Legion to such efforts that the breach was carried and Gate Forty-Two taken. The honour of slaying the Unsighted Kings was claimed by Horus as Imperial Warmaster and at the moment of their execution, the xenos' psychic hold over the population was dispelled. The Akum-Sothos Cluster was delivered and Horus' prize was reclaimed. The cost was terrible, however, as thousands of Raven Guard, the bulk of them Terran-born, had given their lives before the shattered walls of the final citadel.
ca. 001.M31 Cleansing of 28-3 (Laeran) - When the Emperor's Children's 28th Expeditionary Fleet encountered the serpentine xenos race known as the Laer, they saw the potential for a powerful foe. Seizing the initiative, the 28th Expeditionary Fleet attacked their homeworld of Laeran, for Fulgrim saw the blasphemy in allowing a vile alien race to hold the ideal that they were as perfect as the human form. He ordered his Lord Commanders to attack immediately, beginning a war that the Council of Terra predicted would last for solar decades. Fulgrim heard this prediction, and shook his head. In one solar month's time, he promised, the Imperium would rule Laeran. The Laer never surrendered -- their last warriors died fighting in the ruins of their capital city to protect their central temple dedicated to the worship of the Chaos God Slaanesh, where the primarch discovered the mysterious Silver Blade of the Laer. The encounter with the Chaos-worshipping Laer would mark the beginning of Fulgrim's and the entire III Legion's damnation and their turn away from the service of the Emperor.
ca. 001.M31 First Kobolt War, Razing of Thuyela - The 40th Expeditionary Fleet encountered a race of unusually humanoid xenos in Kobolt space who were lethal and proud, and had no interest in human affairs. The xenos' base of operations was a great transparent vessel that sparkled as if it was made of glass, and so was nicknamed by the Imperials "Scintilla City". It was in actuality an Aeldari Craftworld, and was called Thuyela in the Aeldari Lexicon. True to their capricious nature, the Aeldari of Thuyela attacked the 40th Expeditionary Fleet without apparent reason or explanation, and managed to fight the Imperial fleet to a standstill. Fleet commanders called for help, which came in the form of the Space Wolves' 3rd Great Company ("Tra" Company). The Space Wolves decimated Thuyela. It was so completely destroyed that there was nothing left for the Imperial forces to recover or plunder. Horrified by their "allies'" actions, the commanders of the 40th Expeditionary Fleet were disinclined to call upon the Space Wolves for help again, but would do so when they next encountered the race known as the Olamic Quietude.
ca. 001.M31 Second Kobolt War, Suppression of the Olamic Quietude - The 40th Expeditionary Fleet was an expeditionary force of the Great Crusade that was shadowed by an Astartes complement made up of the Space Wolves' 3rd Great Company ("Tra" Company). During the Second Kobolt War, the 40th Expeditionary Fleet met up with the Space Wolves near Gogmagog Beta, pressing fruitlessly into the territory of the cybernetic Abhumans called the Olamic Quietude. The Space Wolves assaulted the orbital docks of the Olamic Quietude's homeworld, and through the utilisation of specialised weapons, stealth and brute force, were able to overcome their elite soldiers, known as "Robusts." With their defences deactivated, this allowed for the follow-up planetary assault on the Quietude's ice-covered homeworld and the inevitable destruction of their civilisation.
000.M30-007.M31 The Chondax Campaign - Shortly after the Triumph of Ullanor, Jhagatai Khan and his V Legion were next sent to the worlds of the Chondax System. The system was comprised of the planets Epihelikon, Teras, Honderal, Laerteax and Phemus IV, the furthest of the outlying worlds. The culmination of this campaign took place upon the world of Chondax, labeled Chondax Primus EX5, 776 NC-X-S by Imperial cartographers, but named "The White World" by the White Scars due to its salt-like earth. The White World was the crucible of the whole campaign, the heart of those Greenskin forces that had chosen to go to ground in the system. The Khan was ordered by the newly-promoted Warmaster Horus to hunt the remnants of the Ork empire destroyed on Ullanor, the last slivers of the Warlord Urlakk Urruk's Greenskins. The brutal campaign lasted six long standard years as the White Scars hunted the remaining Greenskin forces to extinction. It was while at Chondax that the White Scars would first learn of the outbreak of the Horus Heresy and the betrayal of Horus Lupercal. Delayed by the arrival of the fleet of the Alpha Legion, the White Scars would break-out from the Traitors' cordon and begin the long journey back to Terra in search of answers to why Horus had betrayed the Emperor -- leaving multiple Alpha Legion warships as flaming wreckage in the bargain.
001.M31 The Council of Nikaea - There was an increasing concern in the Imperium as the Great Crusade progressed about the use of psychic abilities. More and more often during the progress of the Imperial conquest of the galaxy, the Imperial Army and Space Marines would make planetfall only to find that the populace was in thrall to mysterious powers and unnatural mystics and so-called "sorcerers." These powers were also very akin to those used by the Thousand Sons Legion of the Primarch Magnus the Red. The Thousand Sons had come under criticism for their use of sorcery by some of their fellow Legiones Astartes. The schism grew so great that it threatened the very stability of the fledgling Imperium and so the Emperor Himself had called for an Imperial conclave to resolve the issue once and for all. This conclave was held upon the world of Nikaea, which was intended to determine whether or not the use of psychic sorcery represented a boon or a grave danger to Mankind and the newborn Imperium of Man. The Council of Nikaea was also the trial of Magnus the Red -- for he was accused of sorcery and of introducing sorcerous practices to the Space Marine Legions through the institution of the corps of Librarians. Ultimately the existence of psykers in the Imperium such as astropaths and Navigators was allowed, but tightly restricted under centralised Imperial control, while the potent and unrestricted use of psychic abilities that was defined as sorcery was officially forbidden, as was the use of Librarians by the Space Marine Legions. All existing Librarians were ordered to cease all use of their abilities and return to normal duties as line Astartes following the council. At the same time, Chaplains were established in all of the Legions, using a model provided by Lorgar of the Word Bearers, to ensure compliance with Imperial decrees. Viewing the gathering at Nikaea as his personal trial, Magnus the Red retreats to his homeworld of Prospero admonished, but unrepentant. The psychically-powerful Magnus and his Thousand Sons would continue to study such powers in secret on Prospero in defiance of the Edicts of Nikaea, which would ultimately lead to their damnation by the Ruinous Powers during the early days of the Horus Heresy.