Editing MidHammer 40,000 (section)

===T’au===
The T’au are mostly unchanged at their core, but the state of the Imperium means that the uncompromising “Join or Die” attitude of the Ethereals must alter  to accommodate not getting blammed immediately. They are a lesser threat to the Imperium’s eastern side than in OH (they are not a threat at all in OH to the point most Ordo Xenos Inquisitors don’t even know they exist), and barely constitute a thorn in humanity’s side. However, they are still a threat none the less, and more worlds have been lost to them than in OH (which makes no sense specifically because the Imperium in MidHammer is not a shithole), but this is not as bad as the Imperium has a much easier time compensating for this. They remain as totalitarian and hierarchical, and still trade with Imperial worlds and Rogue Traders on the border of Imperial space, though this is being cracked down upon after The Humbling of Guilliman.

The Damocles Crusade went absolutely horrifically for the Imperium, far worse than in OH. The inflexible Codex Astartes Chapters that got involved, including the Ultramarines themselves, were unable to handle such a tactically adept and technologically advanced threat without the Warmaster's leadership (which makes absolutely zero sense as the Codex Chapters became inflexible millennia after Guilliman was put in stasis, prior they were the most flexible of all). Roboute Guilliman, despite attempting to salvage the situation, was unable to prevent the loss of dozens of Imperial worlds to Tau occupation, under which they continue to languish to this day. The Damocles Crusade is often referred to as The Humbling, and has resulted in the Primarch resigning from the field to study and revise his Codexes in light of his failure. The Imperium continues to be in an unpleasant cold war with the Tau, having many more problems to deal with before full attention can be given to this threat.

Alternately: When the warp storm abated, Guilliman's people found the T'au Empire. The Lord of Ultramar saw in their technology a way to move the Imperium beyond its technological stagnation. He claimed their territory for Ultramar, making them a client state of the Imperium. The T'au resent this, but realize that overt action against the galaxy-spanning Imperium would be suicidal. The former client species of the T'au (Kroot, Vespid, etc.) variously see the Imperium as saviors who freed them from the T'au, a foreign power who can be played off against the T'au, or insolent barbarians who must be made to understand the Greater Good.