War in the Place of Union
The War in the Place of Union was the first time the Tau and Kroot fought alongside one another. Taking place during the First Sphere of Expansion, it saw the Tau aid the Kroot in expelling Orks from their worlds. So effective was the sudden alliance that they withstood a large Greenskin onslaught long enough for reinforcements from Sa'cea to arrive, ultimately wiping out the Orks. After the successful campaign, the Tau and Kroot launched a ten-year offensive that culminated in the liberation of the Kroot homeworld of Pech from the Orks at the behest of Anghkor Prok.