World of Warcraft is absolutely full of trolls -- not the trade chat kind, the actual race. Whether you're traveling the southern continents or icy heights of Northrend, the trolls are everywhere; vanilla WoW and both expansions have all included troll content of some kind or another. The original game had Zul'Farrak, Sunken Temple and then later Zul'Gurub. The Burning Crusade didn't see much of the trolls in Outland (beyond a few settlements, of course), but trolls played a large part in high elf (now blood elf) history and currently plague the Ghostlands. Eventually we saw the release of Zul'Aman, and with Wrath's release, we were introduced to the ice trolls of Zul'Drak and their capital, Gun'Drak.
While there have been vague hints -- stone tablets and other records -- documenting the history of the race, there's very little solid information regarding the trolls. Big events have been documented, but the day-to-day life and the origins of the trolls aren't really addressed beyond "they have been on Azeroth since the beginning." Of all the various troll tribes, only one is playable -- the Darkspear tribe that now makes its home on Kalimdor. The trolls of the Darkspear have not only made a new home for themselves upon Cataclysm's release, but they've also found two new paths to follow; players will be able to choose troll druids and warlocks with the expansion's launch. In order to understand the Darkspear, a closer look at its origins and the origins of one of the bloodiest wars in Azeroth's history is necessary.
WARNING: The following post contains spoilers for the upcoming Cataclysm expansion. If you wish to remain spoiler-free, do not continue.