The Vanishing of the Underfolk

Back before the Shattering, the underfolk - the civilization largely populated by Dwarves. Deep Elves, Kobolds and Gnomes, underwent some great cataclysm - one that left behind only the dwarves that were away from the great holdings, kobolds in their isolated fane in the Dragon Isles, and Deep Elves that were part of several trade enclaives on the surface. Not a single gnome has been seen since.

The Rabbits have what seems to be the clearest picture:

The gnomes of antiquity were largely known as great arcanists and innovators, with their inventions widely considered to be true treasures in the world at large. Coupled with the legendary architecture and craftsmanship of the dwarven people and the savvy of the under-elves, the Underfolk kingdoms were prosperous, if not expansive.

It is said that the gnomes had worked to create a new technology - the Waygate. Intended to change forever how the world was travelled and explored, the Rabbits are reasonably certain something went wrong with the first activation of an ambitious node on their waygate network.

Regardless, the waygates universally failed - often destroying the area around them. And from that point forward? Not a sign was seen of a gnome or most of the dwarves, and the great Underfolk kingdoms were silent.

The Rabbits mentioned some known waygate locations - the Tower of Ivory in Tintagel, the Arcanist's College in Westgate, and the Bardic Collegium in the Silverwood. It is unknown if any part of the Waygate network was present in the Reach.