The Sundering:The Great Library
All wizards and sorcerers are born with an innate talent that allows them to focus and control magic in ways that a vast majority of mortals cannot, because of this they are potentially the most dangerous creatures on earth. A druid maintains the balance of nature, a cleric must follow the commandments of their god, but practitioners of the arcane have no loyalty or code that restricts when and upon whom they may use their powers. The great library serves as an artificial restriction by providing training with and policing the use of arcane magic.
Any child with any magical talent is required to be tested by the Library. Should they prove powerful enough they are taken from their parents and raised in a disciplinary environment designed to facilitate learning and self-control.
The Library itself exists outside of the mortal world in its own pocket dimension accessible only by arcane practitioners at specially designed gates (although more powerful arcanists can access it simply by using enough power).
The Ouroboros are the military arm of the Library in a certain sense of the word. They are wizards trained to hunt down and stop any and all arcanists who use their powers to influence affairs of the mortal world. Although divine magic users could serve the same purpose, and in some ways might even prove superior for the task.