The Great Treachery.
"When does the Treachery of Lorgar end? When I place my hands around his neck and squeeze."
-Ferrus Manus
Imperial Chronologers argue when and where the Heresy of Lorgar, the single most pivotal event of Imperial History, actually ended. For many, the war is considered to be ongoing. Afterall Lorgar, and his cult still holds vast sway over the Galactic North, and the Legions still continue their great conflicts across the borders of the Imperium.
Bela'kor's Monarchian Revolt
An even't whose significance only comes with Hindsight, The Ultramarine's and Word Bearers are required to work together as the entity known as Bel'a'kor, attempts to take the planet in the name of Chaos Undivided. It is believed by many scholars after the fact, to be a ruse on the part of Lorgar, to discourage Gulliman of any suspicion on his end, as well as leave his legion weakened and fractured for Lorgar's final revolt. It was the first of very many false flags and deceptions that left The Imperium of Man reeling from crisis to crisis.
However certain translations of modern Urizenite chroniclers seem to imply something else. That Lorgar had no intention of sacrificing Monarchia for some sort of power play, and that instead Alpharius and Lorgar adjusted their plans to salvage the damage done by Bel'akor. Whether or not these accounts are true or not is uncertain. And in the current political climate of Urizenesh, there would certainly be a movement to undermine the legitimacy of Bel'akor. Implying that Bela'kor has been motivated less by true service to chaos, than by his own wounded ego would certainly be a narrative that Urizen Loyalists would like to see stick to the Anomphalarchs.
Regardless of what the true intent behind this event: be it a ruse on the part of Lorgar, or Bela'kors attempt to redirect the actions of Chaos, the Monarchian revolt represents for many the opening salvos of the heresy, one which would ultimately seal the fate of Ultramar.
The Scouring of Ultramar
"Angron remembers Gulliman's Ultramar - the one we destroyed. The names remain, but The Ultramar of Planners and Philosophers was never rebuilt. He doesn't know...the people have seen much and fought more. They are hardier now, Accustomed to death and invasions... They are used to fighting while weak."
-Typhus the Traveller
When Ultramar learned how truly alone it was in the Universe, and how little the rest of the galaxy would care or come to aid them. From the Betrayal of Calth, the Siege of Macragge and The scouring of Ultramar. The 500 words of Gulliman, indeed everything Gulliman built, was destroyed. Under the machinations of Alpharius, the Night Lords joined The World Eaters and Word Bearers in punishing the supposed secessionist Roboute Gulliman. While the Ultramarines, their Auxiliaries, and even Gulliman himself fought bravely and valiantly, they were not able to save it. Roboute Gulliman died on Macragge, and most of his Ultramarines either dead or Possessed, led by their former Librarius Ptolemy Eugetes.
Perhaps, the legacy of Ultramar would have died here, were it not for the planning and perseverance of its people. Tarasha, a few Ultramarine Reserves, and the people of Macragge were evacuated on a migrant fleet. Surprising many of the traitors and relaying the news of Lorgar's treachery to Terra.
The Iron Cages
"Any resources are appreciated of course Lorgar, But You don't need to summon demons, they will bring their own." - Perturabo.
For Lorgar's Treachery to be successful, he would first have to overcome a major hurdle. Lorgar understood that for all of his prowess and skills, he was not the warrior that his brothers were. In a conventional battle, they were undermatched, and under equipped for a major fight. Alpharius' did his part of disrupting communications, and encouraging false information about the treachery. However that still left the problem of the Primarchs. Here Perturabo, through the aid of "His Patron" proposed his own solution. The Iron Cages. Perturabo would lure the primarchs into planets created to specifically entrap and entomb thm into their own problems.
The Iron Cages had varying degrees of success, but ultimately fulfilled their goal of keeping a successful counter offensive. With much of the leadership trapped, Lorgar and his chaplains had more time to organize and corrupt the now floundering imperial guard. It is said that most of the Imperial Worlds of Segmentum Obscura and Pacificus fell at this time. The Iron Cages were also directly responsible for Horus Lupercal's disastrous campaign at Isstivan.
Iron Cage: Prospero
Whether or not it was an Iron Cage is debatable. As the events of Prospero likely have more to do with Ahriman than Perturabo. However, whether or not Perturabo's hand was involved in it is irrelevant. The assault of Prospero by the Space Wolves ultimately deprived both Magnus the Red and Leman Russ of their legions. With Ahriman taking The thousand sons away from him, and Leman Russ losing his Space Wolves to the bloodlust of Khorne.
The two primarchs eventually did emerge from Prospero, but the end result of their time surviving what was essentially an open portal to the warp inexplicably changed them both.
Iron Cage: Caliban
Locking The Lion in Caliban with a corrupted populous and unleashing the beasts upon the planet was ultimately a failure for the project. While it certainly kept the Lion occupied for a time, the consequences of the Iron Cage had looming implications for Lorgar's project. The Lion was one of the first to be rescued, as nearby vostroyans came to the rescue. However the ultimate destruction of Caliban by imperial forces created a permanent rift between Lorgar and Luther that would eventually lead to an inter-trator civil war.
Iron Cage: Catachan
Catachan was already a hostile world filled with many violent, dangerous creatures. Very little of the planet's natural hostility was Perturabo. However, the creation of orbital defense platforms that transformed the planet into a prison, was his doing. Fulgrim and his Legion were slowly whittled away by the world, and the years spent upon it.
It was not until Sanguinius' rescue that they were able to escape.
Iron Cage: Olympia
Arguably the Most successful of the Iron Cages, and certainly one of the longest lasting. The Homeworld of Perturabo was transformed into the perfect fortress. All of the corners cut in the other Iron cages seem to have gone into Pertruabo's once homeplanet, as the entire planet was rebuilt into a fortress to entrap Rogal Dorn. And entrap them it did. Rogal Dorn and The Imperial Fists were a non-entity in the Great Treachery of Lorgar. A fact that Haunts the psyche of the Fists to this very day.
Iron Cage: Cadia
Perturabo's Magnum Opus, and the cage that exists to this day. It is a fortress without equal. The impregnable walls of Cadia have served as an eternal battlefield since the first Black Crusade, with every soul lost there an offering to Perturabo's Great Patron. Cadia is the bottleneck that halts Imperial raids into the Center of Urizenesh.
The Treachery of Isstvan
While the Leadership of the Imperium was being imprisoned by the machinations of Perturabo and Lorgar, Horus was being fed false information by his confidant, Alpharius. Having been told that The Insurrection of Roboute Gulliman, The Lion, and Magnus was preparing to conquer the galactic north, Horus prepared what forces he could to head them off at Isstivan.
However Isstvan was a trap. Mortarion, Horus, and Ferrus Manus were all abandoned on the planet, forced to contend with orbital bombardments and demonic incursions while their traitorous sons consolidated their power on board their own ships. Eventually the traitors came back for their Primarchs, with both The Sons of Horus and Death Guard capturing their genefathers.
It is believed that the treachery Mortarion endured on isstvan, ultimately drove him into the homicidal arms of The Bloodgod.
The Little Horus Heresy
"'Where are Horus?' They are fulfilling the destiny you left behind." -Erebus to Lupercal
Horus Aximand and The Mournival, under the influence of erebus, positioned themselves as the true heirs to Horus' Legacy. Hoping to gain the favor of Arch-heretic destined for Horus, they took over the Military campaign for Lorgar, and began their scourge of the Galactic north and West. This period of the Treachery is sometimes called The Horousian Heresy or "Little Horus" heresy, is when most of the major battles took place.
The Little Horus Heresy is considered to have ended after the Blood Angels and Night Lords raid on The Vengeful Spirit.
The Long Night
It's a cruel irony of the war that the greatest cause of casualties in the conflict were by loyalists against each other.
As more information about The Ultramari scourge became known to Terra, Konrad Curze and The Night Lords were declared traitors. The Night Lords, angered at the perceived treachery by the Imperium (who they believe ordered the assaults), went on a rampage through the galaxy. Ultimately this raid dragged Jaghatai Khan into a long raid of cat and mouse that covered the entire galaxy.
The Long Night Ended when Curze, for reasons that were not made known until
=][= CAVE VETITI SCIENTIA CAVE =][=
Curze turned himself into The Khan. Corvus Corax, who assisted the Khan in the Subduing of Curze had to abandon the chase early, as Mortarion's assault on Deliverance reached him.
The Martian Civil War
As the battle for the Imperium ravaged on, Mars was hoping to safely buy itself time. After all it had no idea which Imperium it would be talking to next. And so Kelbor Hal, who was believed to have sympathies for the traitors declared Martian Friendly Neutrality in the ongoing Imperial Civil war. This declaration was perhaps the worst of all possible options for the Imperium, as It meant that Mars was openly willing to supply weapons and equipment to the traitor legions.
This declaration also seems to have sent ripples of a schism down the Mechanicum. While Mars itself declared itself neutral, the individual Forge Worlds did not. Belisarius Cawl, a quiet scientist suddenly forced into the realm of politics, declared his succession from Mars, with several Forge Worlds following suit. Mars was now caught in a three way civil war between the Neutrals, Imperial Loyalists and Urizenites.
The Aeldari Raids
The Aeldari Raids were the result of a last ditch effort on the part of Terra. Having heard about the events unfolding across the galaxy, feared the worst, and that terra would not be prepared for war. Having lost contact with so many of The Legions, many feared the worst, and assumed that they had either fallen or joined the traitors.
To make matters worse, the absence of his Praetorian and The Mechanicum Civil War was making it less likely that The Solar System would be safely defensible.
The Government of Terra had no choice but to assume this was the end of the Imperium and make final precautions. Malcador disclosed the information about the Webway gate and its purpose. The Custodes, and Malcador's newly formed Inquisition, were then tasked with doing whatever it takes to finish the gate before the traitors could arrive at Terra.
Thus the raids on the Eldar began. The Custodes and The Inquisition took whatever steps it took, to beg, borrow and steal the necessary components and information for the Webway gate. The actions of The Eldari raids had a short term impact on the Ultima Segmentum, as The Emperor agreed to take a blind eye to Drukhari Raiders in exchange for greater help and assistance. This negligence ultimately besieged Vulkan as he was forced to act alone not only against Lorgar and Luther's Armies, but also against the emboldened Drukhari. Many Imperial world's now helpless against These raids, defected to The Urizenesh in hopes of Protection.
On a greater level, the Aeldari and Webway campaigns are believed to have created a wound between the Imperium and Aeldari. One that over the next 10,000 years would continue to fester until it transformed into open hostility.
The Last Eclipse
"The Lorgar Heresy is The story of Alpharius." - Magnus
The Coup de Grace of Alpharius' efforts. Having successfully played the Imperium, he had left Terra underprotected, and unsuspicious. Worse still, the Imperium had granted Alpharius significant privileges and access, to the point of being made Praetor pro Tempore of Terra. With so many of The Custodes away to finish the Webway gate, Alpharius had the opportunity to perform his master stroke. An Attack on Terra itself.
Using the Defense weapons of Terra, several pieces of Archeotech, and his own cunning, Terra was made a death world. The Planet Luna, with its many Genetic laboratories and large hive cities was completely destroyed. The Atmosphere of Terra, from both the destruction of The Moon, and the devices of Alpharius, was completely destroyed. The Entire population of Terra that was not in a hive city perished almost instantaneously. The Much vaunted Webway gate was destroyed in an explosion that destroyed over a third of the Imperial Palace. And perhaps his greatest claim was to "kill" the Emperor, stealing his heart as an offering to his Patron god Tzeentch.
The days after this dark period, where magnus and the remnants of the Palace Guard struggled to keep the emperor alive was one where the Imperium was considered Dead. The light of the Astronomicon went out, and absolute turmoil reigned over the Imperium.
The First Black Crusade
"In Sotha Novum Lucem Lutheris lucetque Colchis caecat iscitos. Est Tempus Terrae Tyranno Terminavisse. Ergo Ego te dicit Dei Volunt!" - Lorgar
If The Wisest of The Wise had let us move east instead of west, we could have finally snuffed out Vulkan's resistance and united the two realms. If Lorgar was a man who listened to his generals and not his demogogues. Then we could have truly marched to Terra in triumph.
During these dark days after The Last Eclipse, when Terra fell without so much as a shot fired, and The Light of The Astronomicon went out, It was thought by almost all that the End of The Imperium was here.
Lorgar, from his capital of Colchis, called forth The Great Black Crusade. This Great Black Crusade, was supposed to be not a battle, but a triumph. As Lorgar and his great fleet Gathered many of the Remaining planets of The Segmentum Pacificus joined seeing the Imperium as a broken and hollow husk. As did many along the tempestus as well.
While it seemed like it was only a matter of time before the Emperor's dream was finally put out of its misery, the Imperium was saved by its guardian angel. Sanguinius, the Winged Primarch of The Blood Angels had tirelessly gathered as many of the Legions as he could. Gathering the zealots of Ultramar, the Dark Angels, The Night Lords, The Loyalist Death Guard, The Brothers of Abbaddon, The Iron Hands, The Salamanders, The Imperial Fists, and The White Scars, the loyalists prepared their last campaign to halt the great fleet of Chaos.
It should not have been a victory, but through careful planning and clever battles, The Imperium whittled away at the great fleet. Lorgar and his followers, expecting a triumph and not an actual fight, began to break down and turned to infighting. It was here The Vengeful Spirit fell, and Kharn betrayed the World Eaters. Ultramar began its great southern crusade, and The Nightlords began raids into Urizen's territory.
Lorgar had snatched defeat from the Jaws of Victory, and over a series of patient campaigns, the Crusade was forced to turn back, never reaching Terra. The Imperium, while ruined, had time to lick its wounds.
Aftermath of The Great Treachery (Lorgar Letdown)
While the The Results of the Great Treachery could have been much much worse, as far as everyone present was concerned, this was the worst thing that could have ever happened. Many of the Primarchs were unsure how the Imperium would continue, and their faith in the project severely shaken.
Toll of The Great Treachery
"Wolves without Packs, Angels without Halos, Cast from The Parliament, the Raven becomes a Crow." - The Prophecies of Isha
The Great Treachery nearly undid the century-long work of the Great Crusade. Planets brought into compliance were shattered, armies were irreparably broken, and the leadership of the Imperium was forever shocked. The entire Imperium bore the physical, mental, and spiritual scars of the treachery.
Effects
Ultima Segmentum
The 500 worlds of Ultramar went from the apex of development and culture, to a desolated husk.
MacCragge was transformed into a Deathworld, and would remain one until the 38th Millennium
As a consequence of the War, isolation, and misinformation campaigns, Ultramar has now organized itself into a Separate state "Royume d'Ultramar"
The Ultramarines are less than a tenth of their previous strength
The loss of its leadership, the planet of macragge as well as Tarasha and Roboute Gulliman, has permanently humbled their psyche and culture from one of proud unity to suspicion, fanaticism, and infighting
Segmentum Obscura
Prospero was massacred to a man, along with the near entirety of the Thousand Sons Legion,
Exception to this is Ahriman's Prodigal Sons and Iskandor Khayon's Anamisis
The planet was brought into the warp and is now the nest of the Khornate Wolves
Caliban was forced to be destroyed by The Lion
The planet had already been overwhelmed by the great demons,
Over half of The Dark Angels Legion has betrayed The Lion, joining forces with Chaos
Between the destruction of Caliban and the treachery, The rift between The Lion and Luther was a permanent schism.
Olympia's loyalist population was destroyed by Perturabo, the Planet itself was destroyed taking a third of the Imperial Fists Legion with it.
Most of The Segmentum Obscura, and All of Segmentum Pacificus went with Lorgar to form the new Kingdom of Urizenesh.
Segmentum Tempestus
Inwit, once the home planet of Rogal Dorn, has been completely cleansed of all population. Its entire population captured and sold into slavery by Alpharius' Dark Eldar Allies to be used as bait for Perturabo
The Planet of Chemos was completely slaughtered by Mortarion's Death Guard, the planet itself was made into an uninhabited Toxic Wasteland.
Deliverance was massacred and laid waste by The Death Guard before being chased into the Eye of Terror by the Remaining Raven Guard. The Raven Guard to This Day are nowhere to be found.
The Planet of Barbaros was transformed into a shrine for the Blood God. Those loyal were slaughtered alongside traitors in a monument of carnage to Khorne.
Solar Segmentum
Earth is now a death world, thanks to the sabotages of the Alpha Legion
The Atmosphere of the Planet was ignited, killing all of those on Terra who were not dwelling in a hive city.
There is no way to know just how many died in the attack, nor how many more died in the chaos that befell the now isolated hive cities. Untold Trillions are dead.
Despite Fulgrim's best efforts and the finest science in the Imperium, the Efforts to recreate an atmosphere on Terra has only finally taken fruit after 10,000 years.
A large portion of The Imperial Palace was destroyed in a massive explosion that left a continent sized crater.
The Webway gate also lays in ruins from this attack.
The destruction of Luna left the planet into what would eventually become the Ring's of Terra, hampering Fulgrim's Terraforming efforts..
Legion Astartes and The Primarchs
Gulliman was slain by Angron and Lorgar
Rogal Dorn is a broken man and abandons his legion
Leman Russ is a broken man after his legion abandons him to chaos.
Corvus Corax and his entire legion left into the Eye of Terror, never to return.
Magnus and Fulgrim are now legionless and without a home planet.
The Lion, Ferrus, and Horus still harbor the scars of their Mutinies, losing almost half of their Legions to the Machinations of Luther, Erebus, Typhus, and Horus Aximand.
Horus in particular, was horribly tortured by Aximand and the Fallen Mournival.
The Emperor's Children, Thousand Sons, and Space Wolves Legions were completely destroyed.
The World Eaters, Word Bearers, Iron Warriors, Death Guard and Alpha Legion joined the Forces of Chaos.
The Few remaining legions (Ultramarines, Dark Angels, Blood Angels, Iron Hands, and Imperial Fists, Salamanders) have all sustained severe casualties over the long and grueling campaign.
The Emperor
Malcador the Sigilite was killed by Alpharius
Half of The Custodes were killed in the destruction of the Imperial Palace and Assassination attempt
The Emperor of Mankind was devastatingly wounded and is doomed to spend the next millennia in stasis.
The Webway project was destroyed never to be rebuilt
Alpharius stole the Left Eye, Right Hand, and Heart of The Emperor, and offered it to his master Tzeentch.