Ancient Dwarf Empires
During Dark Ages man of the Dwarfs retreated to their ancestral mountain homelands and sealed themselves away from the outside world. They were one of the few civilizations that managed to withstand the chaos of the Dark Ages and preserve the knowledge and technology from before the purge.
There exists evidence that many of the underground Dwarf kingdoms survived, or even thrived for centuries after the purge. Unfortunately sealed off in their mountain forts without contact with the outside world the Dwarfs had to rely on their ingenuity and engineering skill to survive. One after another their sealed off forts fell or faded away. Some were brought down by natural disasters causing fatal cave-ins. Others fell due to famines or malnutrition caused by poor resource management or failing agricultural systems.
Some forts unsealed their gates after a few centuries to renew trade, only to fell pray to external threats they could not have anticipated. For example, the Lost Dwarf Fortress located near modern day Fairhaven seems to have fallen due to a lycantrophy plague: a condition that did not exist before the Purge, and one they were not prepared to deal with.
It is estimated that most Ancient Dwarf Kingdoms fell by the year 800. Only few of their forts have been found so far, and most have been too badly damaged to recover much of the lost knowledge.
The Dwarfs who remained on the surface and braved the Dark Ages along side humans survived, and thrived, though like most races they have lost most of their pre-Purge heritage under the rule of Dark Age tyrants.