The "Fall of the Aeldari" refers to a catastrophic event in the lore of the Warhammer 40,000 universe, where the ancient and advanced race known as the Aeldari faced their own destruction. This tragedy was primarily caused by their excessive indulgence in pleasure and excess, which ultimately led to the birth of the chaos god Slaanesh. As a result of this event, the Aeldari civilization was shattered, with many of their souls consumed by Slaanesh. The survivors were left scattered across the galaxy, forming new factions such as the Craftworlds and the Drukhari, struggling to preserve their culture and existence.