Fall of the Eldar
The Fall of the Eldar occurred over ten thousand years ago and ended the Eldar supremacy inside of the Milky Way galaxy. They were at the height of their empire and held sway over the vast majority of the galaxy. Their worlds were paradises and full of peace and cultural achievement, and then it was all but destroyed.
Even before this time, it had been feared that the Eldar would fall. The Old Ones warned the Eldar about it, but their predictions and warnings were forgotten and ignored over time.
The Eldar came to believe that all races were below them, even so far as calling them barbarians. This proud and arrogant idea was proven by their advanced technology and control of the Webway. They created many beautiful things and lived long lives and when they died, their spirits returned to the Warp. Slowly, the pride of the Eldar overcame their caution and they became ever more proud and arrogant. They had long since outgrown the need for physical labour as their society provided all, leaving them with only their own desires to satisfy.
Many gave in to their hedonistic desires and cults sprang up over the Eldar lands dedicated to the different aspects of arcane knowledge and sensual excesses. Gradually, the Eldar society grew more and more divided by the different cults. The people became more and more corrupt, delving into vicious practises, verging on sadism. Sadistic killers prowled the streets in search of victims, attempting to find new ways to satisfy their needs. It became harder and harder to satisfy their decadent desires so the acts became more violent. Soon the streets were running with blood and the bestial roar of the crowds could be heard throughout the Eldar empire.
However, the degeneration of the Eldar did not go without resistance. Derided as fanatics obsessed with self-denial and suffering by a hedonistic society, many Eldar free from the corruption plaguing their society - from raving madmen to genuine survivalists - fled their homeworlds in assorted spacecraft. After battling numerous dangers in space, and disaster at the hands of natural predators and Ork incursions these 'Exodites' (named from their 'Exodus') settled untamed worlds far from Eldar space, at the fringes of the galaxy. Life was difficult for a people unused to physical labour and self-denial.
As a direct result of this foul depravity, a new Chaos god was spawned, Slaanesh, formed mainly by the Eldar lusts and desires. No other creature of the Warp created had such a violent birth as Slaanesh, or was as powerful or monstrous. For the years before, the Eldar race had been plagued with the images of the sleeping entity. The Eldar slew each other and feasted on the corpses of their fellow kin, while the worlds around them burned. As Slaanesh was born, there was not a single Eldar who didn't feel the pain. With a psionic cry, Slaanesh assaulted the universe and the spirits of the Eldar were drawn from their bodies and sucked into the warp.
The epicentre of the psychic implosion lay within the heart of the Eldar homeworlds where the Eldar population was concentrated. Most of the Eldar throughout thousands of light years died, their spirits sucked into the warp, and many fleeing craftworlds were overtaken. Far from Eldar space, many of the Exodite worlds survived the Fall, though some shared the fate of numerous Craftworlds and the homeworlds. The Eldar were now a scattered race, to be hunted by the Great Enemy for the rest of eternity.