Trolls have usually been portrayed as an enemy, siding with the Warlock Lord on two occasions. They are territorial and have many disputes. The elves and dwarves in general do not have much to do with them. The highest honor that is awarded to a troll is the Black Irix, which Keltset has, and if one has the Black Irix, then they are considered incapable of treachery.
After the Great Wars
After the Great Wars, the trolls settled in the mountains of the Northland.
During the Time of Allanon
During Allanon's time, the trolls were involved in many of the wars, always with the Warlock Lord's side. In the war against the demons, however, the Kershalt Trolls came and gave aid to the elves, proving themselves to be an ally. Also, Keltset, a rock troll in companion of Panamon Creel, helped Shea on his quest for the Sword of Shannara.
During the Federation
The Federation left them alone.