To conquer the isolated worlds cut off by Warp storm activity and the depredations of evil Aeldari pirates.
In 742.M41, the Imperium of Man launched an expedition into the Lizehi Sector.
However.
This expedition proved far more difficult than they had imagined.
As it progressed, they encountered much resistance.
Some worlds were reclaimed, but others had rebelled against humanity after being separated from Terra's control for too long.
More unfortunately.
They discovered that along the edge of the celestial anomaly in Damocles Gulf, an alien race known as the Tau Empire had already infiltrated the region. Numerous factions, Rogue Traders, and planetary governors were entangled with them, preventing the Imperium from dealing with this alien power.
As more and more worlds broke away from the Imperium and joined the Tau Empire.
The Imperium of Man could no longer ignore them.
It launched an expeditionary war against the Tau Empire.
Yet in this war, they severely underestimated the Tau Empire's strength. They regarded the Tau as the sort of inferior heretics they could wipe out at any time, believing their incomparably loyal Astartes fleets and Emperor-loyal naval fleets could crush them just as they had crushed other xenos that resisted the Imperium.
However.
After successfully purging the world of Vies'El, they crossed Damocles Gulf without pause and advanced on the Tau world of Pra'Yen. There, the Emperor's warriors met the most terrifying counterattack. The Tau Empire's retaliation instantly made the White Scars, Ultramarines, Iron Hands, and Emperor's Scythes feel catastrophe looming over them. The Tau were not the weak race they had encountered before; they possessed an entire stellar empire.
And around that stellar empire.
Hundreds of worlds orbited.
At the same time.
Hundreds, even thousands, of allied races emerged within the Tau Empire's sphere of influence.
Meanwhile, the Imperial side