Timeline of the Warhammer 40,000 Universe - Time of Rebirth (ca. M31 - ca. M32): During the Time of Rebirth the Imperium of Man slowly recovered from the destruction and loss of the Horus Heresy. The myriad wars of the Great Scouring were fought in the years immediately after the end of the Horus Heresy and the death of the traitorous Warmaster Horus.For a time after the end of the wars of the Scouring and the retreat of the Traitors into the Eye of Terror, the Imperium knew peace from the corrupted followers of the Chaos Gods. At the same time, many alien species that had been fought during the Great Crusade reappeared in Human space to take advantage of the disruptions caused by the Horus Heresy. They soon plagued the vulnerable worlds of Mankind already prostrate from the destruction wrought by the Heresy.In order to prevent a single person from controlling as much military power as Horus had mastered and eliminate the risk of another large-scale civil war, numerous reforms were enacted at the hands of Roboute Guilliman in his new capacity as Imperial Regent and lord commander of the Imperium to reshape the Imperium's political and military structure. In this way the men and women of the Imperium could face the new post-Heresy realities of an interstellar government where the Emperor was no longer capable of carrying on the day-to-day tasks of interstellar governance.The Imperial Army was divided into the land-based forces of the Astra Militarum, and the space-based forces of the Navis Imperialis, each with a separate chain-of-command structure and bureaucracy. As noted above, the remaining nine Loyalist Space Marine Legions adopted the Codex Astartes written by Guilliman and were split into the many smaller Space Marine Chapters of the Second Founding that were comprised of only 1,000 warriors each along with their own supporting spacecraft and planetary fiefdoms.The era of Imperial peace and reconstruction came to an end when the Orks rampaged across the Imperium on a massive scale from 544-546.M32. The number of Greenskin attacks grew until it became the greatest Ork invasion that the galaxy had ever know, eclipsing even the Ork WAAAGH! defeated by the Emperor and Horus during the Ullanor Crusade in 000.M30, which had earned Horus the title of Warmaster.Nothing was safe from the Orks' primal desire to conquer the galaxy and their widespread advances were only halted when the Imperium resorted to the use of the most extreme measures, at great cost to the Chapters of the Adeptus Astartes. This conflict was remembered as the "War of the Beast." The traumas of this time ked to the division of the Inquisition into separate specialties to safeguard Humanity in the future from further xenos assaults.As such, the Inquisition was reorganised into separate divisions or "ordos," including the Ordo Malleus that was intended to carry on the Inquisition's original mandate to protect the Imperium from the machinations of Chaos and the new Ordo Xenos to defend Humanity against assaults by aliens. The Ordo Xenos was further bolstered by the creation of its Chamber Militant, the Deathwatch, a new Chapter of the Adeptus Astartes comprised of Veteran Space Marines drawn from multiple different Chapters.The byzantine politics of the Imperium took a calamitous turn in 546.M32 in the wake of the War of the Beast in an event remembered as The Beheading when the High Lords of Terra, the successors of the Imperium's original Council of Terra that had been established after the Heresy to administer the day-to-day affairs of the Imperium in the Emperor's name, were slain to the last individual on the orders of Drakan Vangorich, the Grand Master of the Officio Assassinorum.A Space Marine retribution force drawn from the Halo Brethren, Imperial Fists and Sable Swords Chapters tracked the Grand Master to an Assassinorum temple on Terra. The commander of the Astartes strike force was assassinated as soon as he made planetfall, but the remaining battle-brothers carried out the attack without him. Inside the temple they were attacked by 100 Eversor Assassins. Only a single Space Marine, Maximus Thane, the lord commander of the Imperium and Chapter Master of the Imperial Fists, survived to reach Grand Master Vangorich and end his life with a Bolt Pistol.The Imperium ultimately descended into anarchy for a standard century until new High Lords were chosen following an intervention on Terra by 50 Chapters of the Adeptus Astartes led by Agnathio, the Chapter Master of the Ultramarines, who chose twelve new High Lords with his fellow Chapter Masters in a single session of the Senatorum Imperialis.