Indomitus Crusade

The Indomitus Crusade was the standard-century-long Imperial Crusade led by Lord Commander of the Imperium Roboute Guilliman from Terra during the period known as the Noctis Aeterna in the early 42nd Millennium. Its purpose was to defend and reclaim those regions of the Imperium of Man threatened by the surging Forces of Chaos and the threats of xenos such as the Orks, Tau, Dark Eldar and Tyranids in the wake of the 13th Black Crusade and the birth of the Great Rift in 999.M41. The Crusade lasted into the second decade of the 42nd Millennium, coming to an end at the Battle of Raukos. At its completion, Guilliman declared the Crusade over during a great triumphal review and dispersed its military elements across the Imperium, reinforcing many worlds with new Chapters of Primaris Space Marines. In its wake, the Imperium was stabilised from imminent collapse in the wake of the myriad threats assaulting it, though there was no clear victory over those forces that still threatened to exterminate Mankind's light from the galaxy. At the end of the Indomitus Crusade, Guilliman finally returned home to the Realm of Ultramar with Imperial reinforcements. He sought battle with his brother, the Daemon Primarch Mortarion, who sought to add Ultramar to those worlds already claimed by the servants of the Plague God Nurgle during the so-called Plague Wars.

History
After his defence of Holy Terra during the Second Battle of Terra, Roboute Guilliman gathered a new armada that he named the Indomitus Crusade, the largest concentration of Imperial military forces seen since the original Great Crusade over ten thousand standard years before. Along with elements of the Adeptus Custodes, a small contingent of the Silent Sisterhood, and a vast war host of Primaris Space Marines from many newly-founded Chapters of the Ultima Founding and the legions of the Unnumbered Sons, the Primarch set a winding course. Strike forces from over a dozen pre-existing Chapters of Space Marines, led by the Imperial Fists, joined the fleet.

Thus began many new legends as Guilliman travelled to aid beleaguered planets, even beyond the Great Rift into the Imperium Nihilus. These included the Blood Angels Chapter homeworld of Baal, where the Crusade forces helped the Blood Angels defeat the Tyranid Hive Fleet Leviathan during the Devastation of Baal. In other regions of the galaxy, the arrival of the Indomitus Crusade's forces broke planetary sieges and swept away Chaos and xenos invaders alike to bring hope back to the usually desperate and overwhelmed Imperial defenders. It was not long before word began to spread, as all those planets that could still receive astropathic messages hailed the return of a hero out of myth. Once more, one of the demigods of the past fought for the Imperium of Mankind. The Indomitus Crusade would reach its end over a standard century later at the start of the second decade of the 42nd Millennium at the Battle of Raukos. Afterwards, Guilliman would turn his attention to helping his Realm of Ultramar defeat the forces of the Death Guard Traitor Legion and the servants of Nurgle in the Plague Wars.