*Whatever the Mechanicus did at the end of the War Zone Damocles series really fethed up Mu'gulath Bay/Agrellan. The entire Damocles Gulf was set on fire and further Tau expansion westwards has been blocked.

*Survivors from Mu'gulath Bay attempted to flee to the Farsight Enclaves. The Ethereals sent Commander Surestrike to intercept them. After a standoff there was a battle and Surestrike prevailed, but many rebel Tau escaped.

*Ethereal Supreme Aun'va is still dead, but the Ethereals haven't made it public. Instead they have a hologram generator combined with a AI downloaded with his memories and personality. This AI is now effectively leader of the Tau Empire. When one Tau Commander discovers this he ends up rebelling and is basically erased from history.

*The Third Sphere of Expansion ended with the Damocles Blaze. Hive Fleet Gorgon ate everything to the Tau's east, the west is closed, and the Necron Sautekh Dynasty controlled the rest of the Tau's immediate boundaries.

*The Great Rift fethed up a lot of the Tau Empire, eating up many worlds and killing billions. The Tau call it the "Devourer of Hope". This combined with a lack of expansion made the Ethereals worried about the whole Greater Good system sustaining, and they're desperate to find a new way to expand to reinvigorate the Empire

*An Earth Caste scientist Ka'buto (yes that's his name) studied Imperial warp drive technology & old Kroot Warspheres to make a Slipstream Module that creates an anti-matter bubble around Tau ships and allows them to travel at FTL speed (it isn't a reverse-engineered warp drive). This is met with great jubilation and the Ethereals immediately plan a new 4th Sphere of Expansion under Commander Surestrike

*Despite Ka'buto's warnings, the Ethereals had the entire 4th Sphere fleet activate their slipstream engines at once, the mass use of anti-matter creating a massive gash in reality that swallows them all up. The fleet is thought lost, the Ethereals cover up the debacle, and the Slipstream Engines are shelved.



*However the 4th Expedition survived, but was effectively stuck in the Warp for a long but unspecified period of time due to Warp-time fethery. They're assailed by Daemons and much of the crew seems to go crazy. Much of the Tau are put into stasis out of desperation and this seems to allow many to survive. The Tau blame the non-Tau in the fleet for what is going on and expels/murders their auxiliary contingents. At some point, a "nefarious sentience" in the Warp saves them from oblivion and spits them back out into the Materium (it seems like a Chaos God has plans for the Tau). Only 1/4th of the fleet (including Surestrike) survives the journey but they emerge on the other side of the gash in reality right in the middle of Imperial territory many decades after their disappearance.

*The 4th Sphere immediately sent a drone back into the rift they came out of, and it re-emerges on the other side back in the Tau Empire and makes contact. The Tau discover their mass use of slipstream created a wormhole, and it's re-christened into the Startide Nexus. The Tau Empire side of it is heavily defended and fortified while the other side is named the Nem'yar Atoll and many septs are colonized around it. Where exactly the Tau came out of the wormhole isn't really said, besides it being "deep" within the Imperium.

*A new Sphere of Expansion (the fifth) is organized by the Ethereals with Shadowsun (whose been in stasis this whole time apparently) in command, it moves through the Startide Nexus and expands from there. The surviving 4th Sphere Tau are re-integrated into the 5th. The Imperium is completely preoccupied with the disaster of the Great Rift/Noctis Aeterna and the Tau don't encounter any real resistance and overrun a lot of human worlds in addition to battling Orks/Necrons/Hive Fleet remnants.

*The ex-4th Sphere Tau are very traumatized by their experience and operate with a level of brutality that you don't normally see from the Tau. They massacre Imperial prisoners and use auxiliaries as cannon fodder. The last straw comes when they massacre a bunch of Kroot on a colony, causing a large-scale uprising that has to be put down. In the aftermath Shadowsun pushes for consequences and the Ethereals take all non-Tau out of 4th Sphere contingents and the commanders are put through "ritual punishment". Afterwards they are re-assigned to new units or "re-assimilated" to Tau Society.

*Around this time, the Sautekh Dynasty begins a big offensive against the Western Tau Empire

*Farsight returns to Arthas Moloch to mediate for an unknown purpose, immediately calling a new war council after.

*Commander O'Kais from Dawn of War 1 reappears, he's sent to fight Nurgle Daemons/Plague Marines in the Kellik Plague War.

*There's an amusing bit about a huge Ork Gargant that rampages around a Sept, destroying everything at will and mocking the Tau with loudspeakers. The Tau eventually use an advance version of the Pulse ARC Cannon on six Stormsurge suits, having them combine their beams into a mega-blast that finally takes it down.

*The Tau face a major Hrud migration around Vash'ya. The Tau are initially btfo by the Hrud's time fields but they use drones and remotely piloted battlesuits to win the day.

*The Tau meet a new alien race called the Charpactin, fungoids that communicate with ultraviolet rays. Their method of communication is extremely hypnotic and the Water Caste is able to get them to join the Empire in the "Edification Corps".

*The last part of the Tau timeline states that the Death Guard has begun a massive attack on Nem'yar Atoll side of the Startide Nexus. Shadowsun is leading the defense. The Ethereals are terrified that if the other side of the nexus falls the Death Guard will invade the heart of the Tau Empire itself. The situation is described as desperate but is basically a perpetual stalemate now.