Aside from their shadowy origins, it is clear that the night elves came to power soon after their discovery of the Well of Eternity. Despite the trolls' attempts to keep them from expanding their territories, the night elves built up a mighty empire that expanded rapidly across primordial Kalimdor. Wielding fierce magics never before imagined by the superstitious trolls, the night elves had little trouble doing what the evil aqir could never do: topple the two greatest empires in the world.
The night elves systematically dismantled the troll's defenses and supply chains. The trolls, unable to counter the elves' destructive magics, buckled under the onslaught. The night elves proved to be every bit as cunning and bloodthirsty as the savage trolls -- incurring the latter race's eternal hatred and disdain. The Gurubashi and Amani empires fragmented within only a few short years.
Eventually, the night elves were burned by the arcane fires they had sought to control. Their reckless use of magic had lured the demonic Burning Legion to the world. The demons crushed much of the night elves' civilization. Though there are no records to indicate that the Legion attacked either troll civilization, it is likely that battles took place across the breadth of the continent.
At the end of this terrible conflict -- known as the War of the Ancients -- the Well of Eternity imploded. The resulting shockwave shattered the greater landmass of Kalimdor. The center of the continent was blasted beneath the sea, leaving only a small group of broken, single continents.
Thus, great chunks of both the Amani and Gurubashi Empires still exist in the present day lands of Quel'Thalas and Stranglethorn (respectively). The Azj'Aqir kingdoms of Azjol-Nerub and Ahn'Qiraj have also survived in present day Northrend and Tanaris (respectively). Both troll civilizations recoiled from the vast destruction of the primordial world they had known. The dauntless trolls rebuilt their ravaged cities and set about to reclaim some of their former power.