The 'Deluge was the catastrophic flooding of Akhom in Y12498*. Great walls of water inundated the almost entirely coastal nation, washing entire cities out to sea.
The Deluge was not a natural event, but rather was intentionally caused by the azarketi wizard Isfet. Seeking to drive out what she saw as the land-dwelling peoples slowly destroying her ancestral homeland and planning to establish her own watery dominion, Isfet opened rifts to the Plane of Water just offshore from Akhom, exploiting the thin planar boundaries at these locations. Water rushed into the Material Plane, quickly overwhelming the coast with massive tsunamis.
Two years after the Deluge, Isfet was eventually apprehended by the gold dragon Zandroanyx and imprisoned in Atonement, where she has remained to this day. The rifts have since been closed for the most part, though occasionally sailors in the Kilche Sea continue to see inexplicable spouts of water rising from the waves.
After the Deluge, few survivors remained to rebuilt the ruins of their cities. Most departed for new lives elsewhere - many headed south to Rudamun, while others dispersed across the world.