Gnomeregan

From the introduction: Built deep within the mountains of Dun Morogh, the wondrous city of Gnomeregan was a testament to the gnomes' intelligence and industry. But when the capital was invaded by troggs, the gnomish high tinker was betrayed by his advisor Sicco Thermaplugg. As a result, Gnomeregan was irradiated, and most of its inhabitants slain. The surviving gnomes fled, vowing to return someday and retake their home. The adventurers have been sent to retake the once glorious capital of the city of the gnomes from invaders and traitors.