Roboute Guilliman - Plague Wars: After the birth of the Great Rift at the climax of the 13th Black Crusade fractured the Imperium of Man in half, Ultramar came under assault by the servants of the Plague God Nurgle, who had decided to add the whole of Ultramar to his Garden in the Realm of Chaos.Three star systems to the galactic north of Ultramar, the so-called Scourge Stars, were corrupted by the influence of Nurgle and its planets were transformed into staging grounds for the invasion of Guilliman's stellar empire.The worlds of Ultramar were attacked from within and without by Nurgle's forces, including an invasion led by the Daemon Primarch Mortarion and his Death Guard Traitor Legion and the Daemonic legions of Ku'Gath, a Great Unclean One.These so-called "Plague Wars" lasted for several standard years, until following the end of the Indomitus Crusade's first major phase at the Battle of Raukos in ca. 012.M42, Roboute Guilliman, now the ruling lord commander of the Imperium, finally arrived with reinforcements to aid his beleaguered home.Mortarion's already large invasion force, bolstered by mutants and Chaos Cultists from the Scourge Stars, was accompanied by Typhus and his Plague Fleet alongside a Great Unclean One named Ku'Gath who led a host of 7 Greater Daemons of Nurgle called the "Plague Guard". Their strategy concentrated on taking and holding a few of Ultramar's major worlds such as Iax, Espandor and Konor. The Nurglites only launched smaller raids on the more minor worlds of the sub-sector, always withdrawing before any Ultramarines Astartes were deployed.The Espandor System was the first to come under siege. All the worlds in the system other than Espandor itself fell to the Forces of Chaos; the Ultramarines bitterly contested Espandor Prime until they were later relieved. One of the Greater Daemons of the Plague Guard, Qaramas, lead this attack, and his partial conquest of the Espandor System prepared the way for the rest of the Nurglite invasion fleet to surge into Ultramar.Iax was overrun by the Daemons of Nurgle led by Ku'Gath as the bulk of the invasion force came to bear upon it. It had been converted into a so-called "Hospital World" earlier in the conflict to deal with the spread of Nurgle's pathogenic "gifts" across the sub-sector and was therefore susceptible to infiltration by the heralds of Nurgle despite its stringent quarantine measures.Iax would serve as the base of operations for the Nurglite conquest of Ultramar as Mortarion, the Death Guard and the rest of the Plague Guard ultimately concentrated their forces there late in the conflict.Macragge suffered from bouts of Chaos-induced unrest as Mortarion led probing attacks on the Ultramarines homeworld. While this did not lead to any widespread destruction or damage to critical facilities, these incidents caused a drop in civilian morale and forced the Ultramarines Chapter Master Marneus Calgar to waste precious time and resources on peacekeeping missions and displays of force to shore up the morale and confidence of Maccrage's suffering civilians.Typhus and his Plague Fleet overran and captured one of Ultramar's star forts. He was later directed by Mortarion to attack the Ultramarines training world of Parmenio.Konor came under assault by the forces of the Death Guard, their objective to conquer the crucial system and use it as a springboard for a final attack on Macragge itself.After the Battle of Raukos, Guilliman announced his intention to return to his home realm with thousands of Primaris Space Marine reinforcements and drive back the Chaos assault. First, he cleansed the Hive World of Ardium in the Maccrage System of its Death Guard occupiers.In the course of that operation he learned that Mortarion was using the ancient artefact known as the Hand of Darkness to craft Plague Engines that were re-animating the dead and turning them into Plague Zombies. Guilliman destroyed the Plague Engine on Ardium and freed the world from the influence of Nurgle.His next destination was Maccrage itself, his ancient homeworld. He and his Astartes reinforcements, including the Primaris Marines, brought much-needed relief to the weary populace and defenders. Arriving on Maccrage, Guilliman announced that he had made a grave mistake when he had allowed the official borders of Ultramar to shrink so drastically in the days after the Horus Heresy because of his belief that the Space Marines should not rule over large swathes of Mankind.Instead, he reestablished the ancient ruling Tetrarch Council for Ultramar, and tasked its newly-appointed four Tetrarchs, including his Primaris Space Marine Equerry Captain Decimus Felix and the Ultramarines First Captain Severus Agemman, with beginning to expand the territories of Ultramar to include all of the star systems that had once comprised the Five Hundred Worlds.After taking stock of the dire situation, Guilliman reorganised the Ultramarines and their mortal auxilia and launched a large-scale counterattack against the invaders. Several Ultramarines Successor Chapters also joined the fight at their primarch's behest, their Chapter fleets engaging the Death Guard and doing their best to keep Ultramar's shipping lanes and supply lines to the broader Imperium safe and secure.Guilliman first set his eyes on the Espandor System as part of what he named his "Spear of Espandor" campaign, because it served as the main supply line for the Death Guard invasion from the Scourge Stars. He retook each of the lost worlds in the system and destroyed the Plague Engines that were raising the endless tide of Plague Zombies on each of its worlds.After a ferocious battle in which the Ultramarines Chapter found itself fighting side-by-side with their Primaris Astartes brethren for the first time, the forces of Nurgle were routed from Espandor. Guilliman decisively ended the battle by slaying the Great Unclean One Qaramas with the Emperor's Sword and destroying the last Plague Engine in the system. The Espandor System had been cleansed of the taint of the Plague God and the forces of Nurgle were now cut off from their base in the Scourge Stars.With their supply lines to the Scourge Stars cut, their Plague Engines disappearing and slowly eliminating the constant tide of undead reinforcements, and new Imperial reinforcements pouring into Ultramar with each passing solar day, Mortarion found himself on the wrong side of what had become a war of attrition.Guilliman had successfully cut the Death Guard off from resupply and would now proceed to cut their forces to pieces, one system at a time. With this in mind, Mortarion decided to throw all his remaining forces at a single target in the hopes of reversing the tide.Maccrage was still too heavily defended for the forces of Nurgle to carry out a successful assault, so Mortarion decided that the Plague God's servants would target the Ultramarines training world of Parmenio. This battle saw the biggest armoured clash between the Chaos and Imperial forces during the war.The largest star fort in Ultramar, Galatan, attempted to provide support but was engaged by Typhus' Plague Fleet and was boarded by a contingent of Traitor Marines, leading to the death of the Novamarines' Chapter Master Bardan Dovaro in the vicious fighting.On the surface of Parmenio, however, the Ultramarines slowly gained the upper hand. Guilliman killed Ku'Gath's lieutenant, Septicus, and shattered his daemonic Plague Guard, an action that finally gave the Emperor's servants the upper hand in the conflict. With the campaign at last in hand, Guilliman turned to the hunt for his traitorous brother.Guilliman then finally led a relief force to benighted Iax. Having not discovered Mortarion leading his forces on either Parmenio or Espandor, the Lord Commander of the Imperium was determined to hunt down his traitorous brother once and for all.The climactic battle of the conflict took place on Iax, where Guilliman and Mortarion personally fought each other to a brutal stalemate amongst the ruins of the Hospital World. In the wake of this battle, as the Nurglite forces in Ultramar continued to lose ground on every front, Mortarion and the Death Guard were summoned back to the Scourge Stars.Nurgle's outpost in realspace had come under assault from the forces of Khorne in what would become the War in the Rift, another campaign in the endless Great Game between the Ruinous Powers as they maneuvered for advantage against each other.The Death Guard withdrew from Iax under the cover of a Virus Bomb attack on the Imperial forces and Nurgle's remaining servants ultimately retreated from Ultramar, but the threat of a renewed attack from the Scourge Stars was now a persistent threat.