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
