The defeat of the Void Snake simultaneously in 952 AC and 88 AC caused a revision of events around Aurobin-dô. As most of the temporal discrepancies concerned the fate of the dwarves, a majority of the impact was not felt on the Aurobinian mainland—but rather, in the caves below.
It is no secret among scholars that the Void Snake dug the Underdark itself in a single millennial instant, before absorbing all the light within the earth and succumbing to hibernation. Thus, when the dwarves reached its resting chamber, they were already only a few miles from the Underdark proper. Thus, after the historical revision provided them with the leadership and direction to continue digging, they needed only excavate a bit of collapsed and dilapidated tunnel to reach a treasure trove of mineable, uninhabited, undeveloped estate.
The Nirnayak empire became a thing of beauty and power in the Underdark. Most dwarven clans in the Omkar mountains and the Ramcharitmanas were voluntarily absorbed into Nirnayak before they had the chance to be introduced to the Aurobinian humans.
The spread of Nirnayak below Aurobin-dô was not all prosperity, however. Expansion had its price when the dwarves first encountered illithids in the Underdark; the centuries have seen many raids on dwarven centers and outposts, with none returning from the mind flayers’ fortified stronghold. Mining and hunting disputes have also made dwarves an enemy in the Drow, with the two sides harboring a mutually savage and remorseless antagonism.
Some things never change though, and lore remembers a time, some centuries ago, when a young dwarf named Kell sacrificed himself to seal the Toltenon Spiderbane, the blade destined to slay Lolth herself, in a mythic subterranean lighthouse far to the south.