That is just a misinterpretation of what happened. The Humans fought a defensive war where the Trolls who sought to massacre them to the last were neutralised.
And heck, the Humans weren’t even on Troll territory to begin with, they had their own home in the Eastern Kingdoms, it’s the Trolls that tried to kill the Humans to either rebuild their empire or who knows, the Humans retaliated on a similar scale.
Any correlation you may try to draw with the colonisation of the Native Americans is completely absurd.
This isn’t “history written by the conquerors”, it’s Chronicles lore. Which apparently is “written by the Titans’ view”. A third party, that witnessed things as they unfolded.
No, no the same doesn’t go for the Night Elves. It’s silly that you would try to make the current Night Elves guilty of the deeds of the same empire they deposed and later distanced themselves from.
Over ten thousand years ago, no less.
As they should for self-preservation. Those former owners haven’t grown any less violent with the following generations. The fact they are still alive and their villages are still standing should tell you a good bit on the tolerance and restraint the Humans are showing here.