This is an argument I often see, but it’s always missing critical context.
For starters, neither the Elves nor the Humans ‘drove the trolls out of their land’. When the Elves and nascent Humans (both at very different times with the humans arriving centuries before the Elves did) arrived in what would eventually become the Eastern Kingdoms, the Trolls controlled a lot of territory, but there were no clearly defined borders that the Humans at that time, or the Elves would have known about. Maps of that time period, if they even existed, would not have clearly marked boundary lines showing what land was Troll land. They’d be reliant on border markings, if there were any, and they could easily be missed or misunderstood if they were spotted.
So they did not carve a path through the Trolls and take their land by force, they simply found empty land to settle on and did exactly that, they settled. For the humans this was actually not an issue, as aside from the occasional scout, they didn’t run into many Forest Trolls and the Forest Trolls mostly left them alone (there aren’t any notable records within the lore of humans fighting trolls before the Troll Wars). The Elves on the other hand had a much harder time as the Trolls would often attack them on sight. But still, despite the attacks the Elves did not ‘drive the trolls out of their land’ but instead found a place to settle, much like the humans had, and settled.
Unfortunately for the Elves, they happened to settle in an area of the forest that was the site of an ancient Troll city that the Amani considered to be sacred, and that’s what resulted in the constant fighting between the two races.
Fast forward to the Troll Wars and the first thing to note is that they were started by the Amani acting as the aggressors against the Elves. Mind you this was a good 4000 years after the initial conflicts between the Elves and the Trolls over where the Elves settled. The Elves were content, within those 4000 years, to leave the Trolls alone and only dealt with scouts and the occasional raiding party. Mostly due to the fact that the Elves erected runestones to protect their nation from the Burning Legion, which had the side effect of scaring the superstitious Trolls and kept them at bay. The Trolls simply were not brave enough to go near or past the runestones most of the time.
The Troll Wars was the Amani’s first attempt in thousands of years to wipe the Elves out and they failed, but importantly, neither Elves nor Humans wiped out troll villages or laid waste to Troll land (we have no records of that happening). All records of the Troll Wars show that it was a war between armies, not a war of genocide that wiped out villages of non-combatants. They ultimately lost the war at the foot of the Alterac Mountains, but even after the Troll armies were pursued and slain during their route, that’s where the conflict ended. Could the Humans and Elves, united as they were, moved on Zul’Aman and wiped it out? Yes, they could have. Did they? No. Zul’Aman was left untouched after the Troll Wars.
Fast forward to the Second War, and again we see a repeat of what happened during the Troll Wars. The Elves were again only dealing with the occasional scout or raiding party, nothing too serious. There was peace and security in Quel’thalas for the most part. This is confirmed in the Sylvanas book written by Christie Golden. But when the Amani allied with the Horde they began another war of aggression with the aim of wiping out the Elves, and just like the Troll Wars, the Trolls ultimately faltered (mainly because the Horde refused to commit to wiping out the Elves and shifted their attention over to Lordaeron).
As for Zul’jin, he committed severe acts of cruelty and torture against the Elves, so they repaid him in kind when they captured him during the Second War. That’s how he lost his eye. His arm was not actually taken by the Elves, but rather he cut it off himself to escape from the Elves during an Amani raid on the camp where he was being held.
