Legions Incarnate Chronology

The Timeline covers the ending of the Unification Wars, the Great Crusade, individual campaigns of the Legiones Astartes including the discoveries of the Primarchs and will be listing categories of events that followed.

Ending of the Unification Wars (739.M30-798.M30)
The Emperor of Mankind reveals himself following the presumed ending of the Age of Strife, and as the storms that ravaged the galaxy calmed, he believed it was the best time to reveal himself to a desperate humanity and formed the Imperium of Mankind, alongside his closest friend Malcador the Sigillite. The Unification Wars ended with the extermination of the Thunder Warriors, the unification of the various Terran nations underneath the Imperial banner and the making of the Legiones Astartes, or Space Marines.

As Terra fell underneath the Emperor's grasp, change fell quick upon the barbaric states. Civilization returned, at least with the limited resources that Terra still possessed. The Imperial Palace was later entered construction, enlisting most of the planets labor for the task. But as the Imperium gathered its impressive forces, such as the earliest Space Marines and the Imperial Army. The Emperor knew that for the Great Crusade to succeed, he would need equipment and voidships to carry his armies to the stars.

Primarch Project
The Primarch Project, which was initially begun at some point in the 29th Millennium, far beneath the surface of Terra in the Emperor's gene-labs, marked the Emperor of Mankind's attempt to begin the creation of the next generation of Imperial super-soldiers to replace the Thunder Warriors. These were the Primarchs, twenty extraordinary transhuman men who would be His generals -- great warriors, intellectuals and political leaders who would conquer thousands of worlds in His name. Through the machinations of Chaos, the Primarchs were stolen while still in their gestation tubes and scattered across the galaxy. But all was not lost, as the Emperor still possessed their gene-sequences, which He utilised as the genetic templates for the creation of His Legiones Astartes.

The First Founding
Utilising the genetic material from the stolen Primarchs, the Emperor creates the first gene-seed and implants it into his already elite Terran soldiers. These warriors provide the genesis of His Legiones Astartes. The 20 original Space Marine Legions are created during the First Founding. The Legiones Astartes were to spearhead the Emperor's next and grand plan to unify Mankind underneath the Imperium, superior to mere humans and more of a match for xenos that pollute the galaxy.

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. However, The Emperor knew that for the Great Crusade to succeed, he would need equipment and voidships to carry his armies to the stars. The Emperor would later sail towards Mars, and managed to garner the support of the Tech-Priests to coexist in the Imperium. Another interesting thing to note is that the Treaty also preserved the Arcane religion that the Tech-Priests worshiped despite the Imperial Truth. The Mechanicum would add its extensive forces to that of the Emperor's Terran Armies, pitting two powerful engines of war into one superpower. As the Emperor had access to the Ring of Iron that surrounded Mars, he also had the vessels to transport his Legions from the Sol system and beyond to reunify the galaxy in what became the Great Crusade, the crusade that would see the stars burning with battles unending between Mankind and the xenos that plague Mankind.

The Great Crusade (798.M30-005.M31)
The Great Crusade would begin around 798.M30, when the Legiones Astartes utilizing the equipment and voidships developed by Mars and the Mechanicum to realise the Emperor's dream of unification. The Sol System would be subjected to Imperial domination after the defeat of its various native threats and the extermination of the Dait'Tar by the Legiones Astartes, the Great Crusade would expand outward from the Sol System into neighbor star systems, ushering in the Age of the Imperium.

During the Great Crusade, it was inevitable that the Primarchs that had been separated from the Emperor by the Ruinous Powers would be located and returned as the Great Crusade expanded across the galaxy—returning these Primarchs to Terra and ushering them as leaders of the Legiones Astartes. These discoveries are listed in the Primarch Discoveries

Primarch Discoveries (805.M30-981.M30)
Even with access to the vast fleets of starships and military materiel that the Forges of Mars could churn out, the expansion outwards into the galaxy from Terra was slow, primarily due to a lack of the necessary manpower and skilled leadership. Without access to the Primarchs' unique genomes, the time required to create a Space Marine was far longer than ideal. The Emperor was also adamant that all the genetic material for new Astartes gene-seed must come directly from him, to keep the gene-seed organs pure and 100% effective, as mutation had a habit of setting in even at this early date in the Legiones Astartes' existence.Only a short time after he had launched the great expedition to reunite Mankind that he called the "Great Crusade," the Emperor was reunited with one of his Primarchs after his Great Crusade Expeditionary Fleet reached the nearby Hive World of Uris during one of its first journeys through the warp; this was Anax, future Primarch of the Sanctified Sons. Being the first of the Primarchs rediscovered by the Emperor, the first of his sons who had returned to him, the two bonded and Anax was given command of the II Legion of Space Marines, the Sanctified Sons. The following years saw more Primarchs discovered and joining the Great Crusade, with each event heralded with great celebrations on Terra.