ca. 790.M30 Incaladion Conflict - Approximately fifty standard years before the Great Crusade would finally reach the Forge World of Incaladion, after a particularly brutal series of incursions and raids, the Taghmata Omnissium -- the feudal order upon which the defence and military hierarchy of a Forge World of the Mechanicum is based -- finally broke down. In the ensuing strife, the Preceptor-General of Incaladion was assassinated and the Forge World split into warring or isolationist factions, bereft of central control or co-ordination, laying it open to invasion and the devastation which followed. By the time the Great Crusade's advance elements reached Incaladion, it was a global battleground, disputed by a dozen different armies; Mechanicum, Renegade and xenos alike all unleashed atomic fire and yet more savage weapons upon each other. During this time, overwhelmed and vastly outnumbered, the Legio Fureans refused to retreat or retrench, and shattered its blade on foes uncounted until it became only a shadow of its former might, reduced to defending the last forge-fane of its dead regent.
ca.792.M30 The Scattered Primarchs - The Emperor's greatest work of gene-craft nears completion, combining advanced science with otherworldly secrets to create 20 superhuman children -- the perfect generals, pro-consuls and diplomats to lead his Legiones Astartes. These so-called primarchs are second only in power and skill to the Emperor Himself, but shortly before the Primarch Project's completion an unforeseen catastrosphe engineered through the machinations of the Ruinous Powers of Chaos scatters their containment tanks through the Warp to many different Human-settled worlds across the galaxy. But all was not lost, as the Emperor and his scientists still possessed their gene-sequences, which He had utilised as the genetic templates for the creation of His Legiones Astartes.
798.M30 Departure of the Great Crusade - Following the successful conclusion of the Terran Unification Wars on Old Earth, the Emperor launched His interstellar quest to reunite the disparate worlds of Mankind and reforge them into one vast, galaxy-spanning empire known as the Imperium of Man. He intended this unity to usher in a new golden age for all Humanity.
ca. 798.M30 Pacification of the Boetian Lowlands - When the XV Legion was created it was used to quell the few pockets of isolated resistance to the Emperor's rule that remained on Terra during the waning years of the Unification Wars. Boetia was a nation that had existed since the Age of Strife and was chiefly known for holding out against the Unification for a considerable period of time until it was finally forcibly incorporated in the newborn Imperium. When Imperial Army forces were forced to invade the Boetian province to bring them back into Compliance, the Astartes of the XV Legion were sent in to finally crush any further resistance in a brilliant campaign that lasted only six solar weeks. Shortly after achieving this objective, the XV Legion was formally named the Thousand Sons by the Emperor Himself and was sent out into the galaxy as part of His Great Crusade.
ca. 798.M30 The Unheard War - This terrible conflict was fought among the Azurite Stations of Uranus in the days before the Great Crusade broke the bounds of the Sol System. Named for the corroded blue of the inner surfaces of their hulls, the Azurite Stations were a linked crescent of void citadels, home to a collection of artisans and near-space scavengers. The newly Compliant Azurites turned to fueling the Great Crusade as conscripts for the starships of the Armada Imperialis. But soon they faced a threat in the form of the Solar Pirates -- remnants of a confederation of Renegades and mutants. Soon war raged, as the moons of Neptune were embroiled in conflict. The VII Legion heard the cries of the Azurites and assaulted the void stations. 50 Astartes made their way inside where the Solar Pirates had fortified themselves. Sensing defeat, the pirates released a psy-plague -- an ancient weapon thought eradicated during the Unification Wars. In a heroic display of bravery, the Imperial Fists sacrificed themselves so as not to allow the psy-plague to escape the confines of the void station. The Astartes overloaded the station's reactors, causing the installation to explode. The "Screaming" was never visited on Mankind again, and it is said that when the Emperor heard of the sacrifice of the fifty Imperial Fists, He ordered the newly-raised Bell of Lost Souls in the Imperial Palace tolled for the first time.
798.M30 The Great Crusade Begins - With the furthest reaches of the Sol System firmly under Imperial control, the Emperor and his Space Marine Legions begin the Great Crusade. The first Mechanicum Explorator fleets leave the system to reclaim surrounding sectors of what will become the Segmentum Sol, carrying the hopes of Humanity with them.
799.M30 The Vhnori Resurgence - The Crimson Walkers emerge to challenge the Unity of the Panpacific Enclaves. They make use of their unrestrained psychic might to dominate the minds of the populace and animate golems stitched of dead flesh, but are brutally wiped out by the VIII Legion in a campaign which pitches terror against the terrors.
801.M30 Discovery of Horus Lupercal - The first of the lost primarchs is reunited with the Emperor, having spent his formative years engaged in vicious gang warfare on Cthonia, a nearby Mining World. Calling himself Horus, he pledges fealty to the Emperor and is given command of the XVI Legion, the Luna Wolves, spending many years as the Emperor's only returned son and one of His closest confidantes. Highly creditable claims state that the Emperor found Horus personally, the first of His lost sons, but no source specifies the location on Cthonia where the two met. Surrounded in millennia of myths and allegory, the truth of Horus' origins will more than likely never be known.
Unknown Date.M30 Cerberus Insurrection - The XII Legion, the newly-dubbed War Hounds, was tasked alongside the Terran XXIInd Dracos Regiment of the Imperial Army to subdue the asteroid prison colony of Cerberus in the Sol System which had risen up in anarchic revolt in a state of near-continuous rioting and mob violence. Initial attempts to impose order by Terran troops had been thrown back in disarray as it became apparent that among the insurrectionists was a Renegade cadre of outlawed Thunder Warriors, the first genetically-engineered warriors of the Emperor who were long believed dead, calling themselves the Dait'Tar. With many of the Space Marine Legions already assigned to the first Expeditionary Fleets of the Great Crusade and en route to the stars, the Emperor Himself despatched His War Hounds to Cerberus with explicit instructions to reclaim Cerberus colony and carry the Emperor's wrath to those that had defied Him. Within five solar hours, a signal was received from Praetor-Commander Calyb Hax of the XII Legion that Cerberus-Primary had been returned to Imperial Compliance.
ca. 800s.M30 Consus Drift Compliance - The Consus Drift was a belt of stellar debris connected by tunnels made from the metal entrails of shipwrecks. Billions of humans who had been stranded for millennia had made these asteroids their home. The Imperium discovered the Consus Drift by accident, when the 3rd Expeditionary Fleet, under the command of the VII Legion, was caught in the stellar phenomenon known as the Mirror Race and thrown into that region. The Astartes were soon set upon by the Drift Clans -- humans schooled and blooded in the brutal arts of void warfare. Thought the Driftborn fought well, they were no match for the transhuman Legionaries. The commander of the VII Legion gave the people of the Consus Drift an ultimatum: accept Imperial Compliance or face extermination. The Clan Warriors immediately surrendered. The 3rd Expeditionary Fleet left after repairs were made, but not before the Imperial Fists had taken the youngest and strongest male warriors of each of the Drift Clans. Of those who survived initiation into the VII Legion, all were inducted into a single unit; the 356th Company, whose reputation for excellence in out-hull void warfare and starship assaults was without peer.
803.M30 Liberation of Sol (Sedna Campaign) - During the Sedna Campaign, eight full Space Marine Legions are deployed to undertake the destruction of the artificial xenos nemesis world of Sedna on the outer edge of the Sol System, whereupon they expunge an alien faction bound to war by unknown psychic means. In the aftermath, the false world of Sedna falls into silence and is lost to Imperial auspices.
ca. 803.M30 "The Flesh Change" - The Astartes of the XV Legion began to display powerful psychic abilities, which was a welcome development for its Astartes as they sought to further emulate the power of the Emperor. Throughout their long campaigns, the Thousand Sons made extensive use of Sorcerers, and their Warp-derived powers were used to leave whole populations in thrall to their will rather than the Legion being forced to carry out a planetary conquest through a costly full frontal assault like the other Space Marine Legions. But soon, the Legion's joy at their psychic gifts turned to revulsion and horror as a wave of ghastly, degenerative mutations began to affect large numbers of the battle-brothers of the XV Legion. These mutagenic changes were called the "Flesh Change" by the Legionaries, and were much feared, as the spiral of degenerative mutation ultimately reduced a proud XV Legion warriors into a mindless mutant abomination that would later be recognised by the savants of the Imperium as a gibbering Chaos Spawn. The number of active Astartes within the XV Legion soon began to dwindle to dangerously low levels as a result of the ravages of the Flesh Change.