The Troll Wars

In 1096, King Fleshcarver united the troll families and waged war on all settlements in the Themthar Hills. Castle Khozad was completely overrun, home of the Goldhammer clan. Several mines and settlements near Cragsheim were also overrun, and survivors retreated to Cragsheim, home of the Highcrest dwarves. Castle Khozad was never re-inhabited, and settlements near Cragsheim remain abandoned as well.
The Troll Wars ended with the Bridgehugger Accord, a peaceable settlement achieved after support from Corynthe arrived and drove the Trolls back. Stopping short of complete genocide, King Aelfric the Wise crafted the agreement where trolls would be allowed to live as long as they traded a useful capacity - guarding bridges throughout the realm in exchange for fees.