Ultramarines - The Plague Wars: One aspect of the Ultramarines Legion that survived the Second Founding was the close relationship between its Astartes and the populations of the surrounding planets.Even before the coming of the Noctis Aeterna with the birth of the Great Rift in ca. 999.M41, Ultramar faced a series of dire threats. Tendrils of several Tyranid hive fleets drifted inexorably towards Roboute Guilliman's realm. The Arch-Arsonist of Charadon, one of the greatest Ork warlord in the galaxy, led a monstrous WAAAGH! from his anarchic domain with the intent of overrunning the Ultramarines' eastern defences.Yet the greatest threat of them all was that posed by the dark servants of Chaos. A vast horde of Traitors, Renegades, mutants and madmen fell upon Ultramar under the leadership of the foul Daemon Prince M'kar the Reborn during the Invasion of Ultramar.And then came the Noctis Aeterna, and with it wave after wave of Daemon-filled Warp storms. In the wake of these disasters, some of the greatest servants of Nurgle, the Chaos God of plague and decay, fell upon the Ultramarines' stellar realm, seeking to corrupt the bucolic beauty of its worlds. The Plague Wars, as they came to be known, saw some of the greatest battles the Imperium had ever endured, with every inhabited planet of Ultramar suffering a staggering number of casualties.There is some debate amongst Imperial circles as to precisely when the Plague Wars began, or indeed which war zones they encompass. As with all the great works of Grandfather Nurgle, this sprawling conflict has waxed and waned, undergoing periods of festering incubation and temporary remission before flaring to life again just as the warriors of the Imperium believed that victory was finally theirs. Even the origins of the Plague Wars are debated by the historitors of Ultramar, with the earliest accounts of hostilities claimed to have taken place even before the Great Rift split the stars.Whatever the truth, it is known that the Plague Wars as the Imperium understands them have stretched across not only Ultramar -- where the forces of Nurgle have assailed the sons of Guilliman time and again -- but also the star systems to the north of the Ultramarines' stellar realm now known as the Scourge Stars.It was amongst these formerly prosperous worlds that supernatural diseases such as the Crawling Pustulence, Eyerot, the Plague That Walks and the Oozing Pox erupted in riotous profusion after the Great Rift opened. Imperial defence lines were overrun by wave upon wave of trudging plague Daemons and fanatical Chaos Cultists. Corrupt demagogues spewed filth and falsehoods that saw defence regiments turn upon their former comrades before joining the pestilent throng.Everywhere, the droning tally of misery and despair was felt. Corpse mountains burned as Imperial authorities strove in vain to stem the tide of corruption that was drowning their worlds, until at last each planet in turn fell wholly into the grip of Grandfather Nurgle. It was these pox-riddled systems that Mortarion, Daemon Primarch of the Death Guard, claimed as his staging post for the invasion of Ultramar, and from here that he launched his initial veiled sorties before his final offensive commenced.The Plague Wars, too, encompass the conflict known as the "War of Flies." This was the stop-start war of attrition that the Death Guard and their allies fought against the worlds of Ultramar in the wake of the Noctis Aeterna. From Talassar to Iax, Circe to Laphis, the Plague Marines launched their strikes. Some were little more than squad-level actions intended to seed contaminants onto Loyalist worlds or enact ritual sacrifices to destabilise the Imperial defences.Others were full-blown offensives by entire vectoriums of Death Guard warriors, instigated to erode the defences of Ultramar and spread destruction and dismay. Against all these actions the Ultramarines stood strong, rallying swiftly to battle the minions of Nurgle wherever they raised their horned heads.Often outnumbered, typically fighting alongside beleaguered battalions of the mortal Ultramar Defence Auxilia, the scions of Guilliman threw back one attack after another and burned out the corruption of Chaos wherever they found it. Macragge, the Ultramarian capital world, saw fighting across its bleak, rocky uplands as well as in its populated cities. The Ultramarines' sprawling fortress-monastery -- including the shrine in which Roboute Guilliman had lain in stasis for over 10 millennia -- came under concerted attack.The Bubonicus Legions, led by a favoured Great Unclean One known as Ku'gath Plaguefather, seized the nearby Tartella System before descending upon the planet of Iax, a Garden World rich with life. The Espandor System suffered beneath the "Creeping Doom" offensive of Mortarion and his Death Guard forces. On Parmenio a great armour battle took place, and throughout the sub-sector a naval battle raged, with defensive battle stations engaged by a Plague Fleet led by the Death Guard Lord known as Typhus.Even the disciplined tactics and heroic sacrifices of the defenders were only enough to stave off defeat rather than claim victory. Nurgle's followers pushed their befouling offensive forward, contaminating all they touched.Breaking apart his fleet of the Indomitus Crusade after completing the first phase of the operation following over a Terran decade of combat intended to stabilise the Imperium Sanctus, Roboute Guilliman returned to aid his home system. Seeing that his only chance lay in seizing the initiative, the primarch masterminded a brilliant counteroffensive campaign known as the "Spear of Espandor."Rapid counter-strikes and a series of daring boarding actions clawed back many of the foe's gains. Where the disparate Chaos armies fought separately, the defenders of Ultramar supported each other in every way they could, allowing Guilliman to slowly reverse the course of the war and put Nurgle's favoured commanders on the defensive.Utilising their superior numbers, the Chaos forces amassed for a final confrontation upon Iax. There they fought to a standstill, with Guilliman countering every ploy. Ultimately the Chaos forces were forced to retreat back to their staging grounds in the Scourge Stars, making the move off-planet under the cover of the destruction wrought by the dropping of a massive virus bomb.With little time to spare -- for the galaxy remained riven with war -- the lord commander of the Imperium organised the rebuilding of Ultramar, beginning with the defence networks, before leaving once more at the head of a retributive strike force to continue the counteroffensive against the forces of Chaos.