Fate 40k: Pandora Expanse
The Pandora Expanse was originally home to a clad of Tau that seemed to have broken off from the main Tau Empire. How they managed to reach this secluded region of space is not well known, but scholarly texts indicate that they called themselves the Desolate Enclave. What is clear is that they have colonized a number of worlds, including those with original Imperial colonists whom were forced to bend the knee to Tau rule and join the Enclave as Gue’vesa.
However, by the time House duVal and the wider Imperium returned to the Expanse, the Tau were all but gone. And without whatever threadbare infrastructure the Tau were able to provide, many of the Gue’vesa colonies fell into ruin or reverted to a feral state.
What records remain of the Tau give few hints to their alien reasoning or causes of their disappearance. Some scholars surmise that their various factions fell into conflict, leading to their downfall.