Tal'Dorei in the Age of Arcanum

After The Founding gave way to the Age of Arcanum, some among the mortal races continued migrating to the continent that would later be called Tal'Dorei; some rock gnomes traveled over in this era. The first tieflings, having been created in Issylra during the Age of Arcanum, fled from religious zealots and sailed to the continent.
Acek Orattim, priest of Tharizdun, made his base in Gatshadow Mountain, under which Tharizdun had been imprisoned. Through Acek, Tharizdun's power twisted and elevated the mountain, riddled it with a maze of tunnels, and corrupted the surrounding region.
During the Age of Arcanum , the Kuul'tevir society deteriorated as they turned to violence and lost much of their knowledge of magic. The serpentfolk empire's seers had visions of The Calamity's vast destruction, and the serpents sought a way to survive it; they built a magical field of perfect stasis beneath Vos'sykriss and chose their most powerful to slumber until the danger had passed, then emerge and rebuild their empire.
Possibly contemporary with the Kuul'tevir—and in apparently overlapping territory, in the Rifenmist Jungle—was an ancient civilization called the Qoniira Tetrarchy. Their culture rose long before The Calamity and fell either prior to or during and was ancient even to other ancient civilizations of Exandria.