Summary of the Eradication

Mars the greatest of the Mechanicum's holdings quickly drew the attention of the Emperor's Dark Imperium and Guilliman's Imperium Secundus.  War materiel had long slowed to a crawl from the red planet but this was largely unnoticed in the wake of the Isstvan tragedy.  In the wake of the devastation to the Isstvan Legions supplies were critically important.  All the Legions had sent some small force to the Mars to try and secure supplies of arms and armour for their Legions.  Mars however had become embroiled and a war of its own, a war that would become critical to the galaxy and would even outshine the betrayal at Isstvan.

Secessionists and Sundered Mechanicum try to push Imperialists off Mars but are ultimately thrwarted

The heart of the Mechanicum had been torn in two by the Emperor's proclamation and all sanctions on forbidden technology had been lifted. The effects were almost immediate.  Dark and terrible experiments and machines were made by those history would later call the Dark Mechanicum.  Followers of the Machine God that held to the belief that none were able to safely wield such forbidden secrets, known to posterity as the Sundered Mechanicum began raiding and securing all facilities that produced or researched the previously forbidden secrets.  The forces of the Legions that were on Mars as well as elements of the Solar Auxilia and several Militia regiments were quickly brought into the brutal fighting that ensued, each aiding the Dark and Sundered Mechanicum according to their factions or even individual Legions own agendas.  Some Legions just secured what they could and fled the world, most died on that world named after some long dead god of battle in a grotesque prayer to his name.

The Grand Battle of Sarum.  Imperialists try to secure the Forgeworld of Sarum.

The Warmaster and Emperor threw more and more Legions into the crucible of destruction.  Both sides trying to seize the production of the Forgeworld for themselves. The world's strategic importance was beyond that of any other world in the Imperiums besides Holy Terra and Great Macragge.  Soon Secessionists, Imperialists, Paladins, Dark Mechanicum and Sundered Mechanicum were all fighting for dominance.  No single faction was dominant but the ever increasing numbers the Legions poured into Mars could soon prove telling.

Solis Planum.  Imperialists marshal their defence.

During this time Inwit was another bubbling cauldron of discontent.  The Imperial Fists had split roughly equally between the Imperialists and Secessionists.  The Imperialists finding leadership behind Sigismund and the Secessionists rallying behind Alexis Pollux.  Dorn demanded the Legion purge this treachery from its ranks, although did not at thins point take direct personal action.  Despite his tactical genius Pollux constantly found himself on the backfoot the fighting prowess of Sigismund and the added might of Dorn's Huscarls leading to defeat after defeat.

Back on Mars the Coniugatorii first appeared.  Magos from all manner of backgrounds who preached the unity and sanctity of the Mechanicum.  They decried the Dark Imperium and Imperium Secundus as failed and corrupt.  The Mechanicum was the only path to true unity in the galaxy.  The sanctity of the blessed machine in all its forms was the only true course.  It took months to even get the Sundered and Dark Mechanicum to even consider a truce, all the while trying to remain hidden from the agendas of the Legions.  Finally a meeting was announced between the two factions where the terms of a reunified Mechanicum would be discussed.  By accident or design the Imperialists and Secessionists learned of the meeting and were quick to dispatch forces to intervene in their interests.

Night Lords battle in a Martian Agridome

As the meeting began the Legions closed in on the weakly defended Mechanicum conclave.  The Iron Warriors representing the Secessionists and the Alpha Legion and Thousand Sons representing the Imperialists soon began firing upon one another over the top of the conclve.  Needless to say the Dark and Sundered were quick to curse each other for this betray of trust and called in the armies they had secretly held nearby in case of treachery.  The Coniugatorii barely managed to maintain the peace when coded voxes were received from both the Legion forces.  Imperialists and Secessionists would not interfere in the interests of a reunited Mechanicum if their faction was shown favour from the Martians.  Thus began the second phase of the Coniugatorii's plan.  He declared that combine the might of the Mechanicum could overcome the divided might of the fractured Imperium and an Empire of the Mechanicum, unbeholden to anyone else could rise ascendant in the galaxy.  This call to war galvanised the Mechanicum forces who quickly turned on the forces of the Legionnes Astartes and crushed them beneath the hell of the newly reforged Mechanicum.

Legions battle aroung the Mechanicum Conclave

A final pact was needed to secure the future of the Martian Mechanicum and to begin the crusade to liberate the Forgeworlds of the greater Mechanicum.  One of the greatest and darkest treasures of the Martian Mechanicum would need to be secured and brought forth.  The Sundered Mechanicum had early captured and destroyed all knowledge of this most forbidden of technologies.  Each half of the Mechanicum would need to give something to secure the future of the Martian Mechanicum.  Thus the Dark Mechanicum would be told of the location of the artifact and would be assigned to guard it.  However the only Techpriests allowed to deal with the artifact were those of the Sundered Mechanicum, if it was to be unleashed it would be done so by their command alone.  It was not long before the Imperialists and Secessionists learned of this facility and set out to secure the artifact for themselves.

Anarchy ensues over the ruined facility the mysterious artifact is kept in

Once again the offer was made by both factions that the Mechanicum would be left unmolested if they did not engage the Legions.   Treachery marked this battle unlike any before it, the confusion as to who faught whom and who was allied to whom was a spectacle all to itself.  The Sundered and Dark Mechanicum faught alongside each other weary of treachery but ultimately held true.  The Sundered Mechanicum held true to the truce with the Secessionists and did not attack them at all but threw their full might into the Imperialists.  The Dark Mechanicum launched into the Secessionists from the beginning as well as late in the battle attacking their erstwhile allies the Thousand Sons as they moved into a position to attack the Secessionists.  The Secessionists threw divided their might between the Imperialists and Dark Mechanicum whilst the Imperialists split in half as the Alpha Legion and their attending Militia cut into the Thousand Sons.  Ultimately the Mechanicum were successful and despite the death of the Coniugatorii, the Martian Mechanicum declared its independence from the Emperor and the Warmaster.  

tl:dr:
*Mars becomes the next major battleground in the Secession after Isstvan III
*Skirmishes break out between the Dark Mechanicum, Sundered Mechanicum, Secessionists and Imperialists all trying to secure territory and supplies
*as the Legion forces get bled dry more and more Legionnes Astartes are sent to Mars
*the Imperial Fists suffer internal conflict as the Legion turns upon itself to determine if the Legion will side with the imperialists or Secessionists
*the Coniugatorii appears and tries to reunite the fractured halves of the Mechanicum
*2 major battles decide the fate of the Mechanicum
*1st sees the Mechanicum unite fighting off the Legions as a united front whilst the Legions offer a non aggression pack
*2nd sees The Martian Mechanicum reforged as old trusts are betrayed and the Legions lose their allies on Mars

Summary of the Betrayal

What may have in another time been a most shocking and foul betrayal of trust, Guilliman the Warmaster cast aside what loyalty he had for the Emperor, Master of Mankind.  Instead all that could be heard was the mocking laughter of a thirsting god as the Warmaster beheld his terrible actions. 

Warmaster Guilliman had gathered close the allies he could be sure of, Horus of the Luna Wolves, Sanguinius of the recently sanctioned Blood Angels, Angron of the World Eaters and Fulgrim of the Emperor's Children. To these Primarchs he set forth his plans.  The Imperium it was clear had failed, having fallen into infighting and relgious zeal was quickly replacing logic and reason, the Emperor was unwilling or unable to do anything about it.  As such a new Empire would be built successor to the Imperium and built upon her original ideals. This new Empire would be Imperium Secundus and would be begun on a distant world known as Isstvan III. 

Image from Forge World's Horus Heresy Book 1 Betrayal.

Gathering their might the 5 Legions traveled to Isstvan III. A system that had recently turned against the failing Imperium, or the Dark Imperium as Guilliman's followers would term it. Sending down those warriors who's loyalty to the Warmaster may be in question, as the initial attack wave the Primarchs argued over the next phase of the battle plan. Guilliman knew what must be done, he could hardly leave a force with the combined might of 2 Legions at his back. Even if they would be effectively stranded on Isstvan III. Finally his brother primarchs convinced the Warmaster to do the unthinkable. With a heavy heart Guilliman gave the order do launch the bombardment to begin. None of this sat well with Angron who at the first opportunity warned the Legionnaires on the surface of what was coming.  As Guilliman learned of this, he could only give a wry smile. At least some of the Legionnaires would receive an honourable death. 

Angron's warning, although only moments before the bombardment struck was sufficient to allow the Legionnaires on the surface time to prepare. Over a hundred thousand marines died in an instant, and yet, as many survived that terrible betrayal. As the survivors clambered from their hiding spots they saw only the contrails of falling drop pods. At the very least they would have a chance for vengeance!

Many legends were made and broken on the scorched and blackened husk of a world that Isstvan III had become. The Secessionists suffered a terrible toll at the hands of the Imperialists but they were ultimately successful. Almost a quarter of a million Legionnaires had fallen on Isstvan III, the equivalent strength of two full Legions.  From this horrific event the Warmaster emerged more determined than ever to make the future worthy of the weight of the past.

Whatever response the Warmaster expected the Dark Imperium's to have, it is likely he never expected that there would be no response what so ever.  After Isstvan, Guilliman quickly secured those worlds owing fealty to him.  With the combined might of the Legions supporting the Warmaster brought almost the entirety of the Ultima Segmentum under the Warmaster's direct control.  Although Isstvan III had taken many months to finally and totally secure the Warmaster still had the chance to take control of the war.

The Imperium had meanwhile fallen further upon itself.  The self styled Paladins facing off against their brother Legions that were pursuing the extremes that the Legions were now permitted to follow under the Emperor's name.  The removal of sanctions placed upon the Mechanicum had split the organisation into two warring factions, aided by The Dark Imperium and Guilliman's Imperium Secundus alike.  A battle that was turning Mars into one of the most hotly contested worlds in the galaxy.  Finally the Khan, Magister Militum of the Imperium seems to have turned from the goal of preparing the Imperium for war against Guilliman in a personal quest for revenge against Corax and his Raven Guard. 

tl:dr

*Scions of Guilliman, World Eaters, Blood Angels, Luna Wolves and Emperor's Children Legions go to Isstvan III in order to purge their Legions of Warriors not dedicated to Guilliman's Imperium Secundus.

*The Secessionists are ultimately successful on Isstvan III where approximately 250,000 Legionnaires died.

*The Imperialist Paladins fought against the other Imperialist forces, reducing their ability to react to the Betrayal on Isstvan.

*The Martian Mechanicum continues its civil war aided by forces from both the Dark Imperium and Imperium Secundus

*The White Scars savagely attack the Raven Guard, where the naval battles swing in the Raven Guard's favour.

*Jagatai Khan primarch of the white Scars and Magister Militum forsakes his duties of preparing the Imperium against Guilliman's Treachery.

Men of the Helean First

Colonel Curt Auteberry looked over the camp from his command tent. The Halean First Regiment, Blue Company, Blue Platoon had been sent out to investigate the reports of the forge-factories in the deserts of Mars, or to be more accurate, the reports that they had indeed been under attack from some of the Space Marine Legions. Auteberry sighed and signaled Lieutenant Fairbairn to join him. It was time to begin. Fairbairn rushed to the Lord Commissar's side.

"Colonel. Blue Squad, Red Squad, Heavy Weapons Teams Alpha and Beta, and of course, my Squad, are ready for deployment. Green Squad is currently tending to the security requirements of our camp. Heavy Weapons Teams Charlie, Delta and Echo and Special Weapons Squads Foxtrot and Golf are currently on downtime, resting for the night's Sentry duty. We await your command."

Auteberry nodded. "Send Squad Beta to our right flank, Alpha to our left. Take your Command Squad and Red Squad - set defensive positions here" Auteberry pointed to a spot on the map in front of him. "And I will take Blue Squad and make a move for our Primary Objective. If Report Two Zero Alpha is correct, Centurion Vinicius and Squad Balbus should meet us on the field. After you have secured the Primary, we will make a move for the Secondary Objective." Auteberry pointed to another location on the map.

"Sir." Fairbairn interrupted. "Begging pardon sir, who are Vinicius and Balbus?"

Auteberry looked up from the map and saw the look of confusion on the Lieutenant's face. "They are Marines of the Alpha Legion. General Banister has been in contact with the Alpha Legion, and believes that they have a similar mission to us. He personally ensured me that they will assist us to achieve our mission. Which, if all goes according to plan, will allow Red Squad to move upon the Tertiary Objective." Auteberry pointed at a third location on the map.

"Sir, are we expecting any resistance?"

"Reports indicate no less than four Legions, excluding the Alpha Legion, have been active in this region - The Thousand Sons, Night Lords, Salamanders and Raven Guard. We can of course expect to encounter a Mechanicum force if the report is correct. General Banister has declined to pass on any information as to who may or may not assist us in our mission. Centurion Vinicius will be providing the intel upon his arrival at the drop site. Now, unless there is anything else, it's time."

Fairbairn nodded. "Sir, I'll ready the men." He then saluted, and left the command tent, signalling his Squad Sergeant with a very obvious gesture indicating that his presence was required yesterday.

Sergeant Blake Hobster saluted. "Sir, are we ready to deploy sir?" Fairbairn nodded. "Very good sir." With that, Hobster whistled, gaining the attention of Sergeant Edison Michaels of Blue Squad, and Sergeant Beckett Vipond of Red Squad. Both men jogged over to where he and Fairbairn stood. Fairbairn relayed the orders the Lord Commissar had laid out. With that, Michaels and Vipond gathered their squads, whilst Hobster relayed the information to Squads Alpha and Beta. With that Blue Company set off on their Mission.

The Pursuit of Knowledge (part 1)

His search began on the edge of known space, a city long ruined by some unknown invader. Centurion Nevia looked once again to his companion, they had been friends once, long before. “thiiisss waay” came Seeker Matalio's psychic voice, as always a raspy hiss in his mind. They had been working together so long that he wasn't bothered by it any-more. “furrther into the ssity” Matalio said out loud, speaking this time to the battle brothers that stood in a perimeter around him. “the pssycchic sssignal leads furrther in” the battle hardened veteran next to him nodded and began calling orders, within a few moments a full squad had formed up around him. He spoke another two names and the other squads, less experienced but no less professional, began moving cautiously into the ruins ahead of them, in less than a minute the square was empty as the silent warriors continued after the elusive signal.

Far above them Iron Lord Heifestos Cratus looked grim. He stood imposing in the command section of his battle barge, his many subordinates bustling around him. Officially he was in this emperor forsaken system to hunt down some of the miserable outcasts known as the Raven Guard and much of his Clan was doing just that, but in truth he had come searching for a mysterious psychic signal. He looked back to the pict of the planet, the insignificant dust ball of Mallis, its inhabitants dead and gone for a 1000 years. He looked back at the tactical map and frowned. It appeared that the men he had sent to investigate the signal had been engaged. He would have to do something about that, he turned walking back to his grav chair thoughtfully. An absent wave of his hand summoned a Centurion from the edge of the room. “take your men to assist Nevia at once” he said as he sat down “his mission must succeed”

Nevia ducked instinctively as heavy bolter fire stuttered out across the abandoned city. He checked the positioning of his men and the direction of the fire then activated his vox “Sergeant Malaris, analysis of that fire?” he said to the leading sergeant
the vox hummed as Malaris replied in a unemotional monotone. “single stalker class sentry currently engaging us. two squads of ranged combatants definite moving to engage, probable additional combatants melee also moving to engage. Most likely direction of attack from them is the ruined building directly ahead. Feeding you the locations of the definitives now.” the second the report finished Nevia could hear the sounds of bolter fire from his vox. He considered the tactical data for a moment then began broadcasting rapid orders in Heifesian combat cant.

When Nevia awoke he was on a triage cot, in a room with grey metal walls and ceiling. He looked over and spotted a armoured apothecary in iron hands colours at work over another bed. As he got up a medical servitor moved over to him and extended out a screen. It displayed his new orders, that he was required to either consent to transfer to the immortals or to kill himself to erase the shame failing to achieve his objectives. the orders came from Iron Captain Zaus and were countersigned by Heifestos himself. Scrolled after that was a detailed report of the battle highlighting his failing's to counter assault the enemy flamer unit when it got within range, leaving a squad open to three simultaneous assaults and bunching his men up enough that his enemy could ambush him on two sides. Nevia was about to reach for his pistol, though whether to kill himself or the servitor he didn’t know when it beeped again and extended a scroll. He took it and was surprised to find that a single sentence was written on it. “Join the Immortals I still have uses for you” and then Heifestos's signature. He dropped the scroll, maybe there was still hope for him.
“My lord, we have found the source of the psychic signal. It appears to be a marker of some kind.”
Heifestos smiled “Lorekeeper Coeus is on his way. Secure the area and wait for him. Command out.” he said. He allowed himself a short moment of triumph and then opened a new vox channel to the lorekeeper. “Coeus, the marker has been found. Move immediately to examine it and report back to me, we have been on this world too long already.”
there was a bang through the vox and then it crackled to life “already in motion my lord.”

“Amazing, to all sensors it appears to be nothing but stone, but it radiates a psychic aura beyond anything I've ever seen” Coeus stood in front of the tall stone marker, all around him Iron Hands fortified the area. “Forgefather Promethi what do you think” he said looking at the imposing Iron Hand next to him.
“I've never seen anything like these carvings. The age analysis is impossible, literally. The machine is either showing yesterday or a trillion years. When I tried to take a sample to run through my system the servitor exploded. This is definitely not normal stone. Have you tried to psychically probe it yet?”
“not yet, I was waiting for the translation of the writing, which seeing as the cogitator we brought to do just that has been spouting gibberish for the last five minutes and has” he paused as the cogitator exploded in a shower of sparks “just exploded, I guess that wont be happening.” he sighed “well I best start before Heifestos voxes us again. He picked up his force staff and aimed it directly at the marker then closed his eyes and stretched out his mind through the conduit of the staff.

Warzones of the Betrayal (Deliverance Lost)

The Betrayal era sees the Legions the beginnings of the Secession proper.  With several major warzones being fought over between the Secessionists and Imperialists at the dawn of Guilliman's Imperium Secundus.


Shortly before the events of Isstvan III the White Scars were sent to destroy the Raven Guard Legion.  Having taken it upon themselves to censure the ever erratic actions of the White Scars, the Raven Guard found themselves cast adrift, no longer a part of the mighty Imperium.  Whilst determining what course of action to take now Corax withdrew the majority of the Raven Guard back to Deliverance, this one of the Raven Guard's most tragic mistakes during the Secession.  Unbeknownst to Corax the White Scars had been sent to attack his Legion, to punish them further and to rid the Imperium of their newest enemy.  The White Scars attack was sudden and brutal. The White Scars came out of warp mid system, a freakishly dangerous action at the best of times and one that caused considerable damage to the White Scars fleet, they unleashed a terrible devastation on the Raven Guard forces which scrambled to counter attack.
 
Deliverance Lost Rules
The Legions fighting over Deliverance are:
Imperialists
White Scars
Secessionists
Raven Guard

Being one of the longer lasting fights during the Secession, Deliverance Lost will occur over several eras.

There are 3 main theaters involved in the battles of Deliverance Lost.  Players should use these theaters to help them theme mission selection, game size and terrain types.  The three theaters are:
The Desolate Moon

The moon Deliverance is a desolate and blasted wasteland punctuated by the moons defence systems and the few habdomes needed above the surface of Deliverance.  This theater would be good for larger battles and is the only theater where large numbers of tanks and larger vehicles could easily be used.  Rocky outcrops, craters, defensive weapon emplacements and limited buildings would be perfect terrain for the moon.  Planet Strike would be perfect to represent the initial landings on the moon.
The Labyrinths of Deliverance
Beneath the surface of Deliverance lies the vast network of cavernous tunnels of the old Lycaen mines.  Those mines with richer seams or further from the Raven Spire are still used as mines.  The tunnels closer in serve as armouries, storage, training and housing areas for the Legion and its serfs.  Extremely close in fighting, with limited long ranged or aerospace support would make this theater ideal for City Fights or Zone Mortalis battles.  Although larger, more open areas abound Deepstriking, Fliers, and Barrage weapons should be very heavily restricted.
Naval Battles and Kiavahr's Hives
This theater is a mix of battles fought in and amongst the Hives of Kiavahr and the various battles that took place in space between the White Scar and Raven Guard fleets.  Broadly speaking similar terrain and rules could be used for each.  Zone Mortalis and City Fights would be ideal, as would a densely clustered terrain set.  Planet Strike would work for the initial boarding actions in the space battles and the Void War rules (coming soon to a Secession blog near you!) could also be used.

Generic Betrayal Warzone Rules
Although the various Legions are assigned to various Warzones this doesn't mean that elements for their forces aren't active elsewhere in the galaxy.  As such (and so no one gets left out; and we can have some big games)  players may bring their Legions to any Warzone.  There will however be a benefit given for fighting in the correct warzone (more details in a future post).

Warzones of the Betrayal (The Battle for Mars)

The Betrayal era sees the Legions the beginnings of the Secession proper.  With several major warzones being fought over between the Secessionists and Imperialists at the dawn of Guilliman's Imperium Secundus.


Mars is without a doubt the most important forgeworld in the galaxy.  Supplying the vast majority of the Crusade fleets' materiel.  When the Emperor lifted the bans on forbidden technology, the hiccup in supplies was barely noticed.  As what would later be called the Martian Rebellions rolled on disruptions became more common.  Many Legions sent small teams to investigate and secure materiel for their respective Legions.  Before long full blown war broke out on Mars, with the Imperialists backing the Dark Mechanicum and Secessionists backing the Sundered Mechanicum.  The Iron Warriors and Scions of Guilliman knew the loss of Mars would cut the Secession off from vital supplies and an major strategic position.  The Thousand Sons and Alpha Legion sought to preserve the vast knowledge of the Mechanicum and hold the powerful forgeworld. The Thousand Sons were also desperate to prove the worth of the Librarius and over turn the Edict of Nikaea.  The Battle for Mars would prove to be one of the longest running and most vital warzones in the entire Secession.
 
Battle for Mars Rules
The Legions that are fighting on Mars are:
Imperialists
Thousand Sons
Alpha Legion
Secessionists
Iron Warriors
Scions of Guilliman

Being one of the longer lasting fights during the Secession, the Battle for Mars will occur over several eras.

There are 3 main theaters involved in the battle for mars.  Players should use these theaters to help them theme mission selection, game size and terrain types.  The three theaters are:
The Great Forges
 Dotted all over the landscape of Mars are the vast Forges and Manufactorum.  Within these Labyrinthine complexes the tech priests labour to supply the Imperium with their war material.  Cities of death battles would be perfect to represent battles fought withing the vast forges of Mars.  otherwise dense urban terrain would be most suitable.
The Plains of Mars
The vast surface of mars is dotted with ruins and wreckage of wars long past. Smaller supply stations, launching platforms, vast roadways and the few smaller forges that are on the surface of Mars litter this rocky wasteland.  This theater would be ideally suited to larger games especially ones involving lots of vehicles.  Roads, craters, rocky out crops and smaller clusters of buildings to represent supply depos or small installations are ideas for terrain.
The Orbital Platforms 
Space dockyards and supply stations this theater gives some great opportunities for odd battles.  From using the rules for Void battles (which I'll add in an upcoming post) to using corridor sets (like Space Hulk or the many available from various online sellers) to city fights or planet strikes.



Generic Betrayal Warzone Rules
Although the various Legions are assigned to various Warzones this doesn't mean that elements for their forces aren't active elsewhere in the galaxy.  As such (and so no one gets left out; and we can have some big games)  players may bring their Legions to any Warzone.  There will however be a benefit given for fighting in the correct warzone (more details in a future post).

Warzones of the Betrayal (Isstvan III)

The Betrayal era sees the Legions the beginnings of the Secession proper.  With several major warzones being fought over between the Secessionists and Imperialists at the dawn of Guilliman's Imperium Secundus.


Guilliman gathers his closest allies above the blighted world of Isstvan III.  It is here Guilliman, Horus, Fulgrim, Sanguinius and Angron openly plot against the rule of the Emperor.  Their first move to cleanse their Legions of those who show greater loyalty to the throne than to their Warmaster and Primarchs.  It is Guilliman's intention to simply strand their Legionnaires upon the world on which they now fight.  Sanguinius and Fulgrim are quick to point out that leaving an army of that size at their backs is too great a threat.  Guilliman does not hear the plans of his brothers, nor their bickering, his heart is heavy with the knowledge of what he must do.  The orders to begin the bombardment are given, soon the Imperialists in their ranks will be purged in the most ignominious way possible.  Guilliman wears a wry smile as the order spreads from his brothers to their Legions, as he alone hears Angron give the order that the Imperialists be warned of their fate.  Perhaps the Legionnaires will get an honourable death after all, a chance to stand against this Betrayal.

Isstvan III Rules
The Legions that are battling on Isstvan III are:
Scions of Guilliman
Emperor's Children
Luna Wolves
World Eaters
Blood Angels

Isstvan III will follow all the rules found in Betrayal and players are strongly recommended to use the scenarios found therein.  I will be running 3 of the Legendary battles as multiplayer events in the 3rd week, middle of the campaign and as a finale game, more details will be provided closer to the events.

When any of the above Legions fight a battle on Isstvan III their player should decide if they are playing as Secessionists or Imperialists.  It does not matter which side their opponents choose.  When players post their game results (to be detailed in a future post) they will need to add which side they played as. 

Generic Betrayal Warzone Rules
Although the various Legions are assigned to various Warzones this doesn't mean that elements for their forces aren't active elsewhere in the galaxy.  As such (and so no one gets left out; and we can have some big games)  players may bring their Legions to any Warzone.  There will however be a benefit given for fighting in the correct warzone (more details in a future post).

Notable Events of the Great Crusade (part 3)

At the end of the Great Crusade we saw the Chaos Gods claiming the legions that would descend into madness.  The campaign had a pretty simple system in place to track a players overall Loyalty and their victories.  This system was used to determine which of the Chaos Gods would favour which Legions.  In the cases of Khorne, Nurgle and Slaanesh this went pretty smoothly.  For Tzeentch though we had a tie between Salamanders and Thousand Sons.  In the case of a tie it would come down to a roll off between the tied Legions and any Legion that wasn't being played.

The tl:dr at the end will give a quicker overview and say where the differences with the canon occur.
On with the final events.

The Emperor's Children were forever attempting to attain perfection.  This served them well during most of the Great Crusade.  It served to make them an exemplar of tactical acumen lauded by their brother Primarchs.  Towards the end of the Great Crusade their attempts to attain perfection took a darker note.  They would forewarn their enemies of impending attack or even, on one occasion deliberately broadcast their assault plans to the enemy, all in an attempt to attain perfection.  This along with the spreading rumours of the Legion's Apothecaries attempting to perfect the Astartes form, saw the Legion fall out of the Emperor's favour.

The Emperor reveals that he is stepping down from the mantle of supreme war leader of the Imperium to pursue his Great Work.  In his place a new leader will take control of the Imperial war machine, the greatest of the Primarchs and the one that stood closest to his vision of the Imperium, Robute Guilliman!  Where the other Primarchs had turned on each other or devolved to their own petty ideals or squabbles, Guilliman had lead a continuous series of crushing defeats against the Xenos.  To honour Guilliman's achievement the Ultramarines were renamed the Scions of Guilliman.

After the shambles of the battle of One-five-four-four the Iron Hands began to make sure that such weakness would never again seep into the core of the Iron Hands.  This process began slowly but in the true fashion of the Legion it escalated very quickly.  It began with a review of tactical and strategic planning, then they began utilizing the forbidden tech that the techpriests had been given access to on Mars.  This was then quickly followed by them unlocking their own vaults of formerly forbidden technology.  As this technoarcana flooded into the Legion so to did the plan in more and more clandestine fashion.  From the outside their tactics still looked as complex as a brick to the face, each was structured so that foes would be manipulated into stumbling into the path of that brick. 

Masters of psychological warfare the Night Lords kept pushing the boundaries of acceptable warfare by most standards.  Towards the end of the Great Crusade they had taken to focusing heavily on cutting supply lines, stealing, destroying or befouling food, water and ammo dumps and supplies.  Now were populations not just scared to their wits end but they were also falling prey to famine and disease.  It seemed an almost natural next step for the Legion and allowed them to choke worlds dry or back into compliance with startlingly little resources.

The bloody rampage the White Scars were leaving across the galaxy could be seen by all.  Ferociously slaughtering anyone unfortunate enough to be caught in their path.  Their own tactics of being a mobile hit and run guerrilla force began to shift.  They were still the fastest force on the battlefield but now they would just plow straight into an enemy, and tear out the other side.  Once clear they would simply turn back and repeat the process until they had claimed the heads of all their foes.

The Iron Hands are approached by their closest allies, Warmaster Guilliman and Fulgrim who attempt to use their close ties to Ferrus Manus to bring him into the fold of the Imperium Secundus.  Infuriated that his two closest brothers would consider their father's empire to be falling into darkness Manus turned his back on the two, foreswearing his oaths of friendship and informing them that the next time they meet he will kill them.

Tl:dr
-The Emperor's Children become increasingly interested in fighting the perfect war so their compliance rates significantly lower as does their favor with the Emperor.This is one of a number of similar events.
-Guilliman is named warmaster, the Ultramarines become the Scions of Guilliman
-The Iron Hands become corrupted by Tzeentch.  In the canon it is the Thousand Sons 
-The Night Lords become followers of Nurgle.  In canon this is the Death Guard
-The White Scars turn to Khorne.  In canon this is the World Eaters
-The Emperor's Children and Scions of Guilliman try to get the Iron hands to turn to their cause but the Iron Hands stay loyal to their Emperor. 

Notable events of the Great Crusade (part 2)

During the Great Crusade there was a set of rules that helped track a Legions loyalty to the Emperor.  Thus if a Legion fought in a fashion the Emperor approved of, or towards the Emperors goals they became more loyal.  This included fighting of evil Xenos hordes and being heroically outnumbered.  Whilst those that used more unorthodox tactics or were more inclined to follow thier own goals had their loyalty drop.  This included political and actual infighting (represented by games) or going into a fight with a ridiculous amount of resources. 

This system is why some Legions, despite having events that negatively affected their loyalty still came out as very loyal.  The White Scars are a perfect example.  Their loyalty shot all over the place until right at the end of the campaign they managed to drag themselves through as loyal.

The tl:dr at the end will give a quicker overview and say where the differences with the canon occur. Back to the Events of the Great Crusade:

Ever indulgent to the heights of brutal carnage and bloodshed the World Eaters were reknown for their ferocity and the devastation their attacks caused.  During the Great Crusade the came to enjoy their slaughter more than they previously had.  The World Eaters began to take prisoner their stronger opponents, dragging them back to arenas on their mighty warships.  Where once they would wreak their bloody toll as quickly as possible, they have taken to what on the surface would appear to be a greater tactical acumen. Outflanking their foes, dividing held positions and raids; all uncharacteristic of the Legion.  Taking a closer look at the legionnaires it is noticeable that they are building up their anticipation for the final strike, where they glorify in the horror of the slaughter they inflict.

Willing to do whatever was needed to bring worlds to heel before the might of the Imperium the Space Wolves found themselves falling out of favour.  Whilst the likes of World Eaters or White Scars would slaughter any living thing within arms reach the infrastructure of a world was largely left intact.  Not so for the Space Wolves.  Their willingness to use incredible collateral damage as a weapon often meant more time was spent rebuilding the shattered worlds left in their wake, than even a lengthy campaign would have cost from any other Legion.

During the Great Crusade it became known to progressively more Legions that the Blood Angels harbored some secret.  Eventually it was revealed that the IXth had a flaw in their geneseed, that caused them to loose all self control and enter a dark rage and thirst for blood.  The Blood Angels no longer able to contain this secret, were commanded to purge the Legion of all signs of genetaint and to cease all recruitment immediately.  Knowing that this would mean certain death for the IXth Sanguinius refused the order.  The Emperor's response was swift, the Blood Angels would hence forth be removed from active duty, any action counter manning this would see Imperial retribution.

Despite or possibly because of the events on Chogoris the White Scars continue to grow in favour with the Emperor.  Whilst this seems to temper their combat doctrine slightly from the total slaughter that had recently become their new favoured way of war it caused a select few Legions to really focus together.  Calling themselves the True Legions the White Scars, Alpha Legion, Salamanders and Dark Angels saw themselves as being above their brother Legions, an inevitable sign of the trouble that was soon to occur.

After being given some crucial intelligence by Robute Guilliman the White Scars learn that the Raven Guard have been repeatedly attacking isolated White Scars forces and disrupting their communications networks.  The Raven Guard are suspected of instigating the rebellion on Chogoris as well.  The Emperor, furious that one of his Primarchs would take the liberty to censure another Legion, let alone the highly favoured White Scars, declared the Raven Guard to be enemies of the Imperium and gave the White Scars the honour of ridding the Imperium of such a clearly treacherous enemy as the XIXth.

Tl:dr
(summary with some added details)
-The World Eaters are the first Legion to start the path to following a Chaos God,  in their case Slaanesh.  In the cannon they obviously turned to Khorne.
-Like the Thousand Sons the Space Wolves have lost favour with the Emperor and or the other Primarchs
-The Blood Angels are ordered to purge their legion of tainted geneseed, Sanguinius refuses and his Legion is stood down, on threat of being attacked by Imperial forces.  This is broadly analogous to the Word Bearer's being rebuked by the Emperor in the canon.
- The White Scars once again prove the firmness of their loyalty.  This causes the most loyal Legions to band together.
-The Raven Guard are cast out of the Imperium for daring to censure the White Scars.  The White Scars are then sent to destroy the wayward Legion.  This is the equivalent to the events involving the Thousand Sons and Space Wolves in the cannon.

The Martian Rebellions

Kicking off the 2nd era of the Secession we will have the Martian Rebellion.  For the first two weeks we will play smaller games so we can fit more games in to get used to 40k in general and 7th ed specifically.

Fluff
Once the Emperor had chosen his Warmaster to lead the Legionnes Astartes the Emperor retreated to Terra to begin his Great Work.  None knew for sure what this Great Work was or what it entailed, it did little by little start stirring disquiet in the nascent Imperium.  On Mars the greatest of the Forgeworlds of the Mechanicum the Emperor cast aside his own and older sanctions on forbidden technologies.  Many in the Mechanicum leaped at the chance to study such ancient and forbidden secrets, to learn them, make them their own, to control them.  There were those Techpriests that believed that these secrets should remain forbidden, and they took it as their sacred duty to discover, protect and hide Forbidden technologies.

Before long minor skirmishes broke out in various Forges and between the slowly fracturing Mechanicum.  This caused a minor although noticable drop in the resupply of the Legions.  Before long most of the Legions had sent representatives to Mars to see what the reason for the delays was.  Soon all of Mars became embroiled in a raging battle for dominance.  A fight that quickly involved anyone on the red planet.  By the time Guilliman declared his Secession on Isstvan III Mars had become a swirling battleground in its own right.

Rules
*The Martian Rebellions will begin on Sunday 13th July and end on Sunday 20th July (inclusive).
*These rules are optional, you may play the normal Secession Betrayal Era rules if you prefer.
*Armies are capped at 750pts
*You must field: 1 HQ and 1 Troop
You may field an additional:  1 HQ, 2 Elites, 2 Fast Attack, 2 Troops, 1 Heavy Support
*You may take Allies, if you do you must take: 1 Troop
In addition you may field one of the following: 1 HQ, 1 Fast Attack, 1 Troop or 1 Heavy Support
*You may not take an Unbound detachment
*Units may not select dedicated transport options.
*No units may have a starting size greater than 15 models before joined by independent characters.
*Vehicles other than walkers may not be chosen unless their models are no more than 4" wide, long or deep (flyers may not be chosen at all).
*Monstrous creatures needing more than a 60mm round base may not be chosen.
*You may only have 1 unit with any of the following:
  2+Sv;  3+invul; 4+W.
*Your force must include either your chosen Legion or a Mechanicum detachment (Primary or Allied).
*This detachment uses the Ideal Mission Commander and Objective Secured command benefits

Notable events of the Great Crusade (part 1)

For the first year of the campaign I made a series of events to cover some of the important milestones for the Legions in the canon.  The Great Crusade saw us fighting to see who had the honour of becoming Warmaster (won by Steelesamurai's Ultramarines), as such there was initially no Dark Imperium and the Emperor was the great and terrible being we all know and love.

 To keep things interesting the events that turned Legions to the chaos gods did not meant that they had to turn against the Emperor.  I did this because in the canon the Emperor does not seem to have really taken the threat of Chaos that seriously prior to the Heresy and no one noticed 4 Legions starting to fall to chaos.

The tl:dr at the end will give a quicker overview and say where the differences with the canon occur.  On to the events:

Shortly after the Aplha Legion was reunited with their Primarch the Alpha Legion were approached by a xenos council known only as the Cabal.  Nothing is known about what occurred in this meeting although rumours abound. This left the question in the air about where the Alpha Legion's loyalties may lie.  Ever a secretive and unorthodox Legion the Alpha Legion gave a full account of their activities over the course of the Remembrancer Project, information they had previously suppressed.  Their combat record suitably impressed the Emperor, who gave greater favour to the Alpha Legion.

The White Scars found themselves under a considerable amount of scrutiny, especially from the Raven Guard.  Whilst their actions were proving ever more brutal and erratic their effectiveness could not be denied, and they found themselves bordering on censure for their actions and being a favourite of the Emperor.

The Dark Angels and Salamanders fought alongside each other for a considerable length of time forming one of the tightest bonds of brotherhood between any two Legions.  The two Legions proving time and again they were both willing to give up everything for their brother Legion and the Imperium they fought for.  The Lion and the Drake became one of the most popular and best chronicled accounts of any of the Legions during the Great Crusade and gave the two Legions their nicknames of the Paladins of the Imperium.

The Thousand Sons have their methods and combat doctrine called into question, along with the continuous efforts of Magnus to lobby support from his brother Primarchs, sees the Legion fall from the Emperoro's favour and begins the process that will result in the Council of Nikaea.

In one of the most notable, bloody and brief campaigns in the Great Crusade referred to as the Scourge and the Wrack demonstrated what would occur when the Death Guard and Night Lords are capable of when working together.  The two Legions developed a sombre camaraderie that rivaled the Dark Angels and Salamanders.

The White Scars hear that their home world of Chogoris has thrown off the rule of the Imperium and betrayed its oaths to the Emperor and the White Scars Legion.  The Whites Scars take a considerable amount of time to react and it is later assumed that this is due to the actions of the Raven Guard.  Once the White Scars do react they show brutality and savagery beyond that of any other Legion.  In a week of untold carnage they reduced the population of Chogoris down to a mere 0.1% of its number the week before, tens of millions slaughtered.  Those that were "lucky" enough to escape the slaughter were reduced to breeding stock to provide the Legion with the recruits needed to continue.

Tl:dr
(summary with some added details)
-The Alpha Legion follow the Emperor (instead of the Warmaster as in canon) after meeting the Cabal.
-The Alpha Legion's loyalty to the Imperium is called into question and they prove beyond any doubts that they are utterly loyal to the Emperor.  In the canon this event represented Horus assuming, wrongly, that the White Scars would join him.
-The White Scars loyalty to the Emperor is unshakeable.  There were several of these events that represented those Legions that were steadfast in their loyalty to the Emperor in the canon such as the Imperial Fists or Iron Hands.
-Vulkan and Lion el'Johnson become the ultimate brothers in arms each perfectly complimenting the other.  In the canon this represented the bond between the Emperor's Children and Iron Hands
- The Dark Angels prove their loyalty to the Imperium and its ideals are beyond question.  This is the equivalent of when the Iron Hands were tempted by the Emperor's Children to join Horus.
-The Thousand Sons fall out of imperial favour.  There are several events that represent certain Legions being the least popular or left with unsavoury missions in canon such as the Night Lords and Iron Warriors.
-Night Haunter and Mortarion become the greatest (and most terrible) of comrades in arms.
-The White Scars butcher the people of their homeworld after they rebel.  In canon this was the Iron Warriors attack on their homeworld of Olympia.

The Path to Damnation

  Many were the voices that gave praise to the Emperor, that called him divine, godlike.  During the Reunification of Terra and further into the Great Crusade the Emperor denied such claims.  He would lead humanity from the superstitious darkness of Old Night into a new age of enlightenment, a golden age for humanity.  The Imperium of Mankind, an empire built on reason and securing and safe guarding humanities' place in a hostile galaxy.

  At some point the Emperor stopped denying claims of his divinity.  It is unclear why this is the case, perhaps the Emperor simply tired of it; perhaps he sought to embrace the Immaterium and the power he know that lurked there; perhaps he simply traded reason for madness we may never know.  What ever the cause the effects became clear.  The XVIIth, the Word Bearers, ever idolators, were the most vocal Legion claiming the Emperor's divinity.  Each world they brought into the fold of the new Imperium they would make sure was utterly loyal, utterly faithful to their God-Emperor.  Worship of the Emperor spread through the Legions, slowly at first but growing at an ever increasing pace.

  Not all the Legions developed the same levels of faith in the Emperor.  The XIIIth, the Ultramarines and XVth, the Thousand Sons under the reasoned gaze of their respective Primarchs clung to reason as more and more of their fellow Legions developed a greater degree of faith in the Emperor.  These Legions were by no means untouched by faith, especially when compared to their brother Legions.

  When the Emperor declared Guilliman as Warmaster he took the opportunity to begin his Great Work.  What this was is unknown, however it coincides with the reintroduction of the Word Bearers Old Gods amongst the Legions and the populations they conquered.  Rumours began that the Emperor's great work was to indeed attain Godhood.  The wisest amongst humanity began to worry what this might mean for the nascent Imperium, built as it was on the ideals for throwing off the shackles of superstition.

  A darkness was spreading through some of the Legions.  The White Scars became ever increasingly fulled by rage.  Giving up on their old hit and run style of warfare to simply plow into the enemy and inflict as much carnage as possible.  The Iron Hands who had always sought ancient and forbidden technologies and knowledge, began using and unleashing and unleashing to forbidden powers they had come in possession of.  The Night Lords ever the masters of moral destroying warfare, came into their own when the Emperor praised their efforts.  They began to bring greater woes upon their victims, destroying and corrupting food stores, wiping out more with plague and famine than with bolter shells.  Lastly the World Eaters who although consumed by rage found an almost endless pleasure in the mad butchery they unleashed.  They would continue battles well beyond their reasonable ends and hauled scores of prisoners off to their arenas so they could satiate their battle lust when there was no battle on offer.

Tl:dr
(summary with some added details)
-The Emperor stops denying his godliness during the Great Crusade.
-The Word Bearers having never been rebuked for spreading the word of the Emperor sway many of the Legions into worshiping him as a God.  All worlds they conquer are set up as shrines to the Emperor.
-The Word Bearers reintroduce worship of the Old Gods, this also spreads through the Legions, if at a much slower pace.
-Rumours abound that the Emperor's Great Work is an attempt to become a God.  This worries several Primarchs, notably Guilliman and Magnus
-Unlike in the canon the World Eaters, Emperor's Children, Death Guard and Thousand Sons never turn to Khorne, Slaanesh, Nurgle or Tzeentch respectively.
-The seeds are sown for the White Scars to follow Khorne; the World Eaters to follow Slaanesh; the Night Lords to follow Nurgle and the Iron Hands to follow Tzeentch.

Next time:
Notable events of the Great Crusade.

The Great Crusade

The Emperor's Great Crusade launched to unite the scattered realms of mankind under one joint rule, that of the Imperium of Mankind. The Great Crusade would bring a thousand times a thousand worlds into the new Imperium. Most worlds willingly joined the newly forming empire. Many however resisted the attempt to be absorbed into this, the greatest of human empires. They were soon brought to heel for the good of all humanity. Willingly or forcibly humanity was being driven out of the superstitions of Old Night and into a new age of enlightenment and unity.
At the forefront of the Great Crusade were the Legiones Astartes. The Emperor's post human super soldiers. Who would over the course of the Great Crusade be reunited with, and then led by their lost Primarchs, warrior-leaders of God-like stature and ability. As great as the Primarchs and the Legiones Astartes were they were still prone to human failings.

The later years of the Great Crusade ground to a halt as less and less worlds fell into the hands of the Emperor's Legions. It is said that the Great Crusade had taken a quarter century longer to accomplish less than expected by tactical estimations. Many of the Primarchs and their Legions' had formed close bonds tying them closer together. The Salamanders and Dark Angels; Thousand Sons and Raven Guard; Death Guard and Night Lords are exemplars of the Legions drawing together and forming tight brotherhoods otherwise unrivaled amongst the Legions. Petty rivalries and outright hatred had also simmered amongst the Legions. Between the White Scars and Raven Guard; Thousand Sons and the Luna Wolves; between the World Eaters and the Salamanders and Dark Angels. Entire Expedition Fleets ground to a halt by a refusal of various Legions to work together or all independently trying to perform the same mission but without a single battle leader. In the worst situations various Legions took to warring each other. It was not uncommon for challenges or even small skirmishes to break out between the Legions, or their Primarchs, but when Legion made war on another Legion that was a serious matter.

The Secessionist Legions under the leadership of Warmaster Guilliman.

Image modified from Forge World.


Two of the best documented cases where the Legions seriously attacked each other during this time are refered to as the "Death of the Lion and Drake" and "The Raven's Judgement". The Death of the Lion and Drake recants the tail of how a sizable force of Dark Angels and Salamanders, which earned accolade after accolade for they were truly the Emperor's finest, came under a sudden and brutal attack at the hands of the Luna Wolves and World Eaters. The Dark Angels and Salamanders once they became aware of what had befallen their Legions retaliated in force until they believed their due in the blood of their enemies was paid. The Emperor publically shaming the World Eaters and Luna Wolves and lauding the Salamanders and Dark Angels simply added to the ill will between these Legions. The Raven's Judgement on the other hand follows the hubris of Corax and his Raven Guard. Simple animosity between the White Scars and Raven Guard led to frequent skirmishes. However the Raven guard undertook a secret war of censure upon the White Scars who they had deemed to be straying from the Emperor's grace into a path of mindless bloodshed and rage. The White Scars conquests had earned Jaghatai Khan great favour in the eyes of the Emperor. It was at this point, during the rising glory of the Vth Legion that disaster struck for the Raven Guard. The XIXth Legion's actions against the White Scars was discovered, and their chosen methods of war ever suspect, the Raven Guard were cast from the Emperor's Light and banished from the Imperium of Man. The Raven Guard were not the only Legion to lose their way. The IXth, Sanguinius' Blood Angels had developed a major flaw in their geneseed. They were quickly ordered to stop recruiting and hand themselves, Sanguinius included, over to the Emperor's genomancers to have their geneseed cleansed. Knowing that this would likely be a death knell for his Legion Sanguinius refused, and as a result he and the entirety of the IX Legion declared enemies of the Imperium.

During all this turmoil and unrest there was one Primarch who diligently followed the Emperor's vision. Who almost singularly amongst his brothers fought not with the others but turned back the tides of foul Xenos that beset the Imperium from all sides. Already the master of the Realm of Ultramar, Guilliman of the Ultramarines conquered world after world binging those that his Legion would protect and recruit from into the fold of Ultramar and the remainder to the fold of the Imperium. Although his accomplishments were initially overlooked in favour of the Khan, Magnus, Vulkan and El'Jonson; Guilliman's Realm of 5,000 worlds, Ultramar, and his endless accomplishments saw him elevated to the rank of Warmaster, first amongst the Primarchs. The Ultramarines were also renamed the Scions of Guilliman in his honour. It was tasked to Guilliman to rally his fellow Primarchs and continue the work of the Great Crusade whilst the emperor undertook his Great Work.

The Imperialist Legions followers God Emperor of the Dark Imperium.

Image Modified from Forge World.

For a time Guilliman managed to get the Great Crusade back on track.  It soon became apparent to the Warmaster that all was not well in the Imperium. A festering canker had taken hold at the heart of the Imperium. The Word Bearers began preaching the divinity of the Emperor. Despite Guilliman's scorn no censure came their way.  Guilliman came to view this as the beginning of the corruption the Imperium of Man.  More and more legions echoed the divinity of the Emperor, now openly hailed as the god Emperor. The spread was worse amongst the populace of the Imperium. Only on the worlds of Ultramar did reason hold out against faith. Few were the Legions that did not regard the Emperor as godlike, both amongst those in the Emperors favour and those who had fallen out of favour. It is said at this time Guilliman became disheartened, the Crusade had faltered once more. The chosen of the Emperor saw this as their time to take the title of Warmaster unjustly denied them. A mighty clash between the Warmaster's loyal Legions and the followers of the God-Emperor showed Guilliman what he must do. At the height of the clash he once more commanded the respect of his brothers ordering them to do their duty and give over their petty rivalries. Such spurring oration had rarely been borne witness to before. Ashamed of their actions the Legiones astartes once again resumed the Great Crusade. All the while no word was heard from the Emperor.

Guilliman now strengthened his Legion and Ultramar, now often referred to as the Imperium Secundus, which spanned over half of the Eastern Fringe uncontested. He gathered close his brothers that were spurned by the Emperor, and those already allied strongly with his Legion. He showed these Legions the canker at the heart of the Dark Imperium. How the Emperor had forsaken reason on what seemed a quest for Godhood. How more and more Legions slipped into baser forms of themselves. Upon the world of Isstvan III Guilliman gathered his most trusted allies.  On this isolated system 5 Legions assembled, The Scions of Guilliman; the Emperor's Children; the World Eaters; the Blood Angels and the Luna Wolves.  It would all begin in the Istvaan system, there they would cleanse the elements of their Legions whose loyalty lay with the Dark Imperium, and then Launch their secession from the Imperium of Man, to create the Empire of reason it was truely meant to be. The Imperium Secundus!

Largely unknown at this time the Emperor had released the Mechanicum form its pacts and sanctions on forbidden technologies. This caused growing dissent within the Martian Mechanicum, soon to spread through all the forge worlds. Two distinct factions formed within the Mechanicum. The Dark Mechanicum, favouring the use and exploitation of the previously forbidden technologies. The Sundered Mechanicum who held to the tenants that some technologies were by nature corrupt and twisted and as such should remain forbidden. These two halves of the Mechanicum would come to fight alongside the Dark imperium and the Empire of Ultramar respectively.



tl;dr
(summary with some added details)
-all the legions started infighting before the 'heresy'
-the great crusade took ~25 years longer than canon
-Guilliman is Warmaster, the Ultramarines are now the Scions of Guilliman
-Emperor retreats and starts his Great Work
-Blood Angels and Raven Guard declared enemies of the Imperium
-Word Bearers spread the word that the Emperor is a god and are never rebuked like in canon
-more of the Imperium worships the Emperor as a god, only Ultramar and a few other legion's don't follow suit.
-Word Bearers slowly reintroduce worship of their old gods alongside worship of the Emperor
-The Emperor removes the sanctions placed upon the Mechanicum allowing them to explore previously forbidden tech.
-The mechanicum slowly splits into two warring factions: the Dark Mechanicum loyal to the Emperor and the Sundered Mechanicum Loyal to Guilliman
-The Council of Nikaea bans the use of Psykers within the Imperium.
-a great battle between the nascent sides or the Seceession erupts only to be ended by the oratory of Guilliman
-Guilliman fortifies Ultramar into an autonomus Empire and gathers the Legions loyal to him at the Istvaan system to begin the first true steps of the Ultramar Secession!