Halo's Scourge Invasion

The Halo's Scourge Invasion was a xenocidal campaign that lasted for nearly four centuries that was fought between military forces of the Imperium of Man and the Hel-kar-daxes xenos. The Imperial's primary counter-attack was spearheaded by the Marauding Eagles Space Marine Chapter.

History
This massive campaign lasted for four centuries, from 333-746.M35. Emerging from deep into the Halo Stars, a immense fleet of xenos called the Ascended Council of Hel-kar-daxes, began conquering the region and making way to the passages leading to the Imperium. They reduced in slavery any and all species they conquered, including humans. The whole Marauding Eagles Chapter gathered and began a long and thankless war against the invaders. Théodoric, called the Great, crafted a century-long plan to stop the momentum of the xenos by bypassing them and delving for their coreworlds, only to disappear again.

The two following centuries saw the xenos trying to consolidate their gains, while the Marauding Eagles struck at their ports, use their Scouts to fan the flames of rebellion on human-occupied worlds. Revolts and unexpected attacks forced the xenos to spread their forces. The Brotherhoods were then unleashed on the weakest worlds, reclaiming them and leaving when those worlds occupied by other aliens. The final hundred years saw the rebels (both aliens and humans) steal weapons and starships and wage war against the Ascended Council. Théodoric gathered the full might of his Chapter, roughly 545 Battle-Brothers and attacked the core-worlds. The Ascended Council was annihilated, and its whole population was killed.

The remaining centuries of M35 were spent destroying the aliens uplifted by the Council's technology and brought Imperial compliance to the pagan worlds inhabited by Mankind.