Ascendants: The Second Rebellion
The Emergence was the rise of the orcs out of the Underdark by the will of Gruumsh. During this uprising the orcs swarmed within the carved out cities of the mountain elves, slaughtering many in their wake.
The Emergence forced most mountain elves out of their homes, requiring them to seek help from neighboring human settlements. But instead of help, the elves found themselves in shackles and mass graves. This ensured the quick extinction of the race.