Revolution
Led by the Elves, the younger races fought back against the Yuan-Ti to gain freedom.
The Yuan-Ti, having enslaved almost all the world's other mortal races, were living high and mighty in their temples. However, their slaves, led by the Elves, staged a revolution: twenty years of war followed, the slaves of nearly every Yuan-Ti city rising up to oppose their serpent masters. In the aftermath, the world was free of the Yuan-Ti, and the younger races were ready to take over.