Scouring
The Scouring is the name given to the cataclysmic event that occured when a "flaming mountain" (meteor) fell from the sky, causing massive earthquakes. It landed just off the coast of Gelderland, but the shockwave was so powerful that it caused massive cave-ins in the Underdark, killing all of the dark elves almost simultaneously. Left with no worshippers, Lolth, deity of the dark elves, lost her divine spark and perished. The divine spark then took up residence in an elven werewolf named Elshawen, residing in Midwood at the time. At that point she ceased being mortal and became the Goddess Elshawen, with the portfolio of Change, the Moon, Women, and Lycanthropes.
The Scouring was so cataclysmic that the humans decided to begin numbering their years after it, so that year became 1 AS. The current year is 560 AS. For more information, see the timeline.