Age of the Imperium

The Age of the Imperium is the name given by Imperial lexographers and historians to the period of human history that represents the present time in the Warhammer 40,000 universe. The Age of the Imperium began in the 30th millennium when the Emperor of Mankind emerged from long centuries of obscurity to unify Terra beneath his rule and end the terrible suffering and civil conflicts of the Age of Strife. The Emperor forged a political and military alliance with the Mechanicus Cult that had reunified the Forge World of Mars beneath its rule and together the two most populous worlds of humanity forged the Imperium of Man. Using the advanced technology of the Mechanicus, the Emperor created the twenty Space Marine Legions of the First Founding to launch the Great Crusade, an attempt to reunify all the human-settled colony worlds across the galaxy under a single government once more.

=== The Rise of the Emperor (c. M31)===

During the Age of Strife the great Warp storms that heralded the birth of the Chaos God Slaanesh from the Fall of the Eldar had separated Terra from its interstellar colonies and plunged all the human civilizations across the Milky Way Galaxy into disarray and chaos. When the storms abated with the emergence of Slaanesh in the Warp, a new leader for humanity known only as the Emperor emerged on Terra, the ancient homeworld of mankind. He conquered the raging warlords of late Age of Strife Terra and entered a military and political alliance with the Cult Mechanicum on Mars. With his twenty Legions of genetically engineered Space Marines created from the the genetic material of the Primarchs, the Emperor planned to reunite all of mankind beneath his benevolent rule, banishing the violence, superstition and injustice that had ruled humanity during the Age of Strife.

=== The Great Crusade (c. M31)===

The Great Crusade lasted for 200 standard years and brought many long lost star systems into the fold of the newborn Imperium of Man. Under the War Council of the Emperor and his rediscovered Primarchs, vast Expedition Fleets comprised of the Imperial Army and the twenty Space Marine Legions fought back aliens, feral humans tribes, petty human dictators and the Warp-tainted forces that had gained control of large portions of human-settled space during the Age of Strife. Once a human-settled world had been pacified, it was brought into "Imperial Compliance" by a new Imperial Planetary Governor chosen by the Emperor and it was often occupied by a unit of the Imperial Army that was left behind to complete the integration of the planet into the Imperium while the Expedition Fleet moved on to its next target.

=== The Horus Heresy (c. M31)

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The Great Crusade ended with the nightmarish Imperial civil war known as the Horus Heresy. The Warmaster Horus, the greatest among the Primarchs, leader of the Luna Wolves Space Marine Legion and the most favoured son of the Emperor, fell under the influence of the Ruinous Powers of Chaos. In an attempt to usurp his creator and take his place as the ruler of mankind, Horus took control of a third of the entire Imperium's armed forces (including a full half of the Space Marine Legions and much of the Imperial Army and the Adeptus Mechanicus) and marched towards Terra where his forces laid siege to the Imperial Palace. He was ultimately slain aboard his own flagship during a daring assault by Loyalist forces, but the Emperor was mortally wounded in the final battle and was forced into a state of semi-consciousness on the cybernetic life support system known as the Golden Throne. The Imperium was left rudderless and at the very brink of collapse following the Heresy.

=== The Age of Rebirth (c. M31 - c. M32)===

During the Age of Rebirth the Imperium of Man slowly recovered from the Horus Heresy.

The wars of the Great Scouring were fought in the decades immediately after the end of the Horus Heresy and the death of the Warmaster. In a lengthy campaign the Imperium's forces hunted and banished the remaining Traitor Marines from human space. Eventually the Chaos Marines and the Ruinous Powers' other followers found refuge in the massive Warp incursion known as the Eye of Terror.4 At the same time many alien races that had been fought back during the Great Crusade reappeared in human space to take advantage of the disruptions caused by the Horus Heresy and plagued the vulnerable worlds of man.2b

In order to prevent a single person from controlling as much military power as Horus had and eliminate the risk of another large scale civil war, numerous reforms were enacted to reshape the Imperium's political and military structure. The Imperial Army was divided into the land-based forces of the Imperial Guard, and the space-based forces of the Imperial Navy, each with a separate command structure and bureaucracy. The remaining Loyalist Space Marine Legions adopted the Codex Astartes written by the Ultramarines' Primarch Roboute Guilliman and were split into many smaller Space Marine Chapters that were comprised of only 1,000 men each along with their own supporting spacecraft and planetary fiefs.

=== The Forging===

The Forging is also sometimes known to historians of the Adeptus Mechanicus as the Golden Age of the Imperium.

During this period the Adeptus Terra brought the most important human-settled star systems of the galaxy that had not been reached by the Great Crusade under Imperial control and expanded the interstellar borders of the Imperium. Internal stability was gained with the establishment of Astropath Choirs on countless worlds which allowed a reliable network of interstellar superluminal communication to function using the power of an Astropath's telepathy to send and receive mesages across light years. This period also saw the most rapid advancement in the Imperium's technology and interstellar economy due to the rediscovery of many valuable STC databases from the Dark Age of Technology as the Imperium expanded.

Once more the Imperium repelled the forces of Chaos, heretics and aliens alike across the galaxy and reclaimed many lost regions for the human race.

=== The Nova Terra Interregnum (c. M35)

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The Nova Terra Interregnum is also known as the Time of the Twin Empires and it lasted for 900 hundred years.

During this period the rebellious Ur-Council of Nova Terra dismissed the authority of the High Lords of Terra and claimed separate rule over the Imperium's Segmentum Pacificus. After almost a

During the Cataclysm of Souls which occurred in 975.M35 the Ecclesiarchy tried to transform the Imperium into a theocracy and usurp the power of the rest of the High Lords of Terra. Their efforts ended only in stirring up massive religious wars against the Ur-Council who were denounced as heretics against the will of the God-Emperor. This religious rebellion on many worlds of the Segmentum Pacificus ultimately overthrew the Ur-Council and restored the rule of the High Lords over the entirety of the Imperium.