The wars began in the 860s.M30 when the vicious Rangdan species of Xenos invaded the frontiers of the nascent Imperium. Invading from the galactic north and east, the Rangdan inflicted losses on the Imperium on a scale that would not be seen until the Horus Heresy. Whole Expeditionary fleets went to their deaths without a single survivor, worlds were laid waste, dozens of Titan Legions were obliterated, and entire Space Marine Legions were said to be lost to the Imperium. Much of what happened during this conflict is unclear, 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 purges that left entire human inhabited sectors lifeless to ensure what was hoped to be a final victory. The Rangdan were vicious foes and even their ships were capable of causing heavier losses than they endured against the Imperium in 1 on 1 combat.
Second Rangdan Xenocide
During the Second campaign in 881.M30, an incident known as the Majind Torc Transgression took place when a Basemekanic Barq broke the Imperial blockade of the galactic northeast to make impact at Majind. The Death Guard was mobilized to decimate the activated Macrobeest within by unknown means. Only the quick thinking intervention of the VIth Legion prevented disaster.
Third Rangdan Xenocide
The most well-known stage of the conflict was the Third Rangdan Xenocide in the 890s.M30. This campaign was led by the Dark Angels under their Primarch Lion El'Jonson. During the campaign, the Dark Angels prevented the total destruction of the northern Imperium but suffered devastating casualties, losing 50,000 Battle-Brothers. The losses the Dark Angels endured eventually contributed in them losing their status as the largest legion to the Ultramarines.
During the later stages of the war a member of the XXth Legion identifying itself as Alpharius but admitting their primarch had not yet been discovered came before the Lion. This "Alpharius" offered aid to the Primarch against the Rangdan in hopes that the Dark Angels would maintain their prominence and thus one day The Lion would be made Warmaster. The Lion at this time did not even know of the title Warmaster, but still secretly believed that such a title may one day be likely bestowed by one of the Primarch's by the Emperor. Alpharius stated that the XXth Legion would prefer The Lion be Warmaster over someone like Roboute Guilliman, as he was not so different from them in their views of war and secrecy. It is not ultimately known if The Lion accepted Alpharius' help or not, though the Rangdan were destroyed shortly after. In the aftermath of the battle, the Space Wolves assisted the Dark Angels in purging the remaining Rangdan from the northern Imperium.
- 1: The Horus Heresy Book Seven pgs. 81–82
- 2: The Horus Heresy Book Five pg. 96
- 3: The Horus Heresy Book Three pg. 82
- 4: Scions of the Emperor (Anthology) - First Legion
- 5: The Horus Heresy Book Eight pg.16