Rangdan Xenocides

The Rangdan Xenocides was a series of xenocidal campaigns carried out against vile xenos threat known as the Rangdan Cerabvores during the 860's in the 30th Millennium during the latter years of the Great Crusade. These wars were the most terrible of any yet fought by the Expeditionary Fleets of the burgeoning Imperium of Man. The threat was only stymied after the intervention of the Emperor Himself and at least three Space Marine Legions, over a dozen Legio Titanicus Titan Legions, several Imperial Knight Houses, Mechanicum forces and hundreds of thousands of troops of the Imperialis Auxilia.

History
When the Imperial Expeditionary Fleets of the Emperor's Great Crusade at last had breached the Eastern Fringe of the galaxy, they inadvertently attracted the attention of the Rangdan Cerabvores, a species of such macabre power and technological might it seemed, for a time at least, that the Imperium had met its doom. Facing waves of attack from the galactic east and north, and suffering losses that would not be exceeded until the dark days of the Horus Heresy, the wars of the Rangdan Xenocides were the most terrible of any yet fought. Whole Expeditionary fleets went to their deaths without a single survivor, worlds were laid waste, dozens of Titan Legions were obliterated and by the end, entire Space Marine Legions (exactly which Legions was purposely redacted from Imperial records) lost to the Imperium. Much of what happened during this abyssal conflict is still locked under seal, but what can be said is that with the breaking of the Labyrinth of Night by the Emperor, the threat was at last stymied. What remained was for the Rangdan taint to be purged in a subsequent decade-long series of bio-pogroms that left entire human inhabited sectors lifeless to ensure what was hoped to be a final victory. It was then given to the Space Wolves of the VI and the Dark Angels of the I - the latter who had suffered themselves so very dreadfully against the horror - to conduct these purges, these two Legions entrusted above all others to do what had to be done.

The Titans of the Legio Gryphonicus as well as the Legio Vulturum, the Legio Kydianos and other Xanithe Mechanicum forces of Xana II, served alongside the vaunted Dark Angels Legion during this vital campaign. The Dark Angels hurled themselves at the enemies and broke their greater strength in countless battles against the vile xenos on the edge of the Halo Stars. This campaign culminated in the Third Rangdan Xenocide around 890.M30, which resulted in the loss of the lives of 50,000 Space Marines spent in preventing the destruction of perhaps the entire northern Imperium by the menace from the outer darkness. Due to these extensive losses suffered by the I Legion, by 899.M30, the Ultramarines Legion were on the cusp of becoming the largest Space Marine Legion, standing at around 166,000 Legionaries

Horus Lupercal and his Luna Wolves Legion, who had been otherwise occupied in the ongoing wars in the galactic west, were now firmly in the ascendance in the eyes of the Great Crusade, and with him and those other Legions who retained their strength having not suffered at the Rangdan's hands did the future of the next few decades of conquest and expansion now rest.