Revolution
Arcane magic is discovered. The exact details remain obscured by time but scholars broadly agree on the following: Artefacts of innate power were left behind by deities, discovered by the humanoid races, and studied for their properties.
Every culture claims to have found the first artefacts, often called The Arcane Keys. Initially, understanding was limited and learning was slow; only a special few were able to wield the divine tools. Discovery begot discovery, and so wielders of the arcane began to accrue power, wresting it away from those who ruled by brute strength. Less talented mages reached into the unknown, seeking enhanced power at any cost. New, twisted entities were created in a magical arms race.