The Gurubashi trolls were once the greatest empire of jungle trolls in the world, rivals to the great forest troll empire of Zul'Aman to the north and a power to be reckoned with. Their tens of thousands of years of history have seen wave after wave of humiliation, defeat and loss, and they are without a doubt responsible for much of that defeat. They have consorted with powers not to be trifled with and driven their neighboring troll tribes into slavery or exile.
The empire of the Gurubashi, centered in their great city of Zul'Gurub, was founded after the great war with the Aqir that forever divided the insect state into the distant northern Nerubians and the southern Qiraji. While this defeat was near-total for the arthropod empire, it also fractured troll society forever. Before the war, the Zandalar tribe had stood preeminent, although it was the Amani and Gurubashi who led the charge against the Aqir. Theirs was the hereditary rulership of all troll tribes, theirs was the way of scholarship and it was to them that the hereditary priesthood of the trolls derived its furthest development.
Yet none of these facts could prevent the division of the trolls. After the war, a weakened and shaken Zandalar tribe found itself no longer the center of troll society. It still ruled the ancient birthplace of all trolls, it was still respected ... but the power had forever shifted to the Amani and Gurubashi, and it was not to shift back for tens of thousands of years.
(Spoilers for the Zul'Gurub 5-man are in this post.)