There is a little bit on the history of the Descent and such in
2e's FOR2 Drow of the Underdark but not nearly as much as you might expect. Less than a page.
Here is from page 46:
The history of the drow in the Realms is long and grand, but very murky to the sage or interested inquirer of today. Truth has been willfully twisted by clever and fanatical drow to serve many partisan noble House interests and the major drow faiths. It is usual in Lolth-dominated communities, for example, to pretend that traitors to the Goddess, or vanquished noble Houses, simply "never existed." Although this is a hollow deceit at the time, it effectively "rewrites history" by four generations later. The history of the drow can thus only be recounted in general terms—following the work of Shahaerynus, a drow sage who dwelt in long-ago Myth Drannor, and compiled The High History of the Drow. What you are about to read are excerpts from this book. Susprina, Elminster tells us, is currently working on a sequel.
The Descent
We know very little of the Ilythiiri, or "Elves of the South," before this crucial event. Even then, they were known as "Dark Elves," for the hue of their skins. They dwelt in the jungles and hot forests of the South. A proud, warlike, culturally advanced (some sages of other elven peoples say "decadent") folk, the Hythiiri attacked all neighbors, including other elven tribes. Their cruel raids and depredations, ordered by warlike nobility and the clergy of their two cruel deities, Ghaunadaur and Lolth, forced elves, humans, dwarves, and others to ally against them.
Defeated in a series of titanic magical battles, the dark elves fled into underground warrens they had earlier discovered. This event, known as "the Descent," marked the end of the drow as a surface-dwelling race.
The Dark Wars
The warlike drow nature did not change when they escaped their surface foes. They immediately launched a series of wars to establish territories in the Underdark. They began by stealing and seizing dwarven magical items, and using them against the dwarves—establishing an enmity that is still strong today.
The drow then fought among themselves, noble against noble, priest against priestess, for rule of their new realm. This all-out war ended amid great magical explosions that brought down the roof of the largest dwarven cavern they had seized, great Bhaerynden. The ceiling collapsed entirely, burying many drow and the shattered dwarven cities. The cavern, now open to the sky, became known as The Great Rift. The surviving drow nobles gathered what people, slaves, and equipment they could seize, and fled into the Underdark in search of places to dwell. "The Scattering" brought about the many rival, self-interested cities where most drow live today.
