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this was a minor crusade with 2-3 companies of Astatrtes and a few regiments of Guard, now imagine something akin to Macharius push...

Transport messaging can be faster than you think - at most it's 8 hours + transit time to deliver messages. Likely only 4 hours + transit time. And Tau Messenger ships are the fastest ships they field. Tau FTL may not be rapid response, but it is reliable. Where the Imperium may have different ships in a fleet or flotilla show up at different times because of the vagaries of the warp, a Tau fleet will show up in unified force.



That's the rub, isn't it? A hive fleet is still largely vulnerable in space - and that's how Shadowsun broke the splinter that came at the Empire - in space where Tau can hammer them with long range salvos. The Tau communication method isn't blacked out by the Shadow in the Warp - so reinforcements can be called easily enough. Of course the main push of a Hive Fleet would annihilate the Tau... but why would the main thrust of a hive fleet pass through a backwater in the eastern fringe?

Likewise, while the Imperium has the manpower to eliminate the Tau, it doesn't have the spare forces to do it. Damocles was a weak crusade because there's just so much else going on that's more important than a tiny alien empire on the far eastern fringe. Can't pull troops from here, or here or here because there's 3 different Waaagh!'s raging through, Cadia needs more equipment, and Armageddon is still in flames. Can't pull sector fleets because of increasing incursions by Necrons, Eldar, and Dark Eldar. Hive Fleet splinters are everywhere, and the latest bunch of gribblies looks like it's pushing for Terra. Chaos legions are still active and the Imperium is still dealing with the aftermath of Abbadon's latest failure. The Tau Empire is just so unimportant compared to the legions of threats the Imperium faces that it's going to remain largely unmolested.

Well, in a 40k world mere survival is a proof of potent force (cough, Eldar of any allegiance). I cant deny Tau are quite efficient at running their compact Empire. It's just that they dont have (yet) the tech needed for Galaxy-spanning one (long range warp travel/comms of the Imperium, Eldar Webway while it was still operating).
Tau might somehow technically master the warp yet (AI navigators? psi-transceivers?). But it they fail, they will never be able to form more than loose confederation of isolated colonies, much like pre-Imperium humans.
As for the Tyranids and backwater Eastern Fringe, both Bhemoth and Kraken were coming from that direction... had Behemoth veered off a few degrees it could have hit Tau instead of Ultramar. (ouch!)

whoever makes GW the most money.. thread over....

In a Galaxy spanning war not much happens very fast.

Tau to Terra: We'd like to do our utmost to avoid war.
first relay: We'd like to do avoid war.
second relay: We'd like to do a void war.
third relay: This means war!

We're not going to make it Brookman! The signal will never get through! I'm freaking out man! Chaos.. Chaos everywhere..