Unions

Keyblade wielders chose to join one of five Unions once they had managed to form a keyblade. These Unions were Unicornis (headed by Foreteller Ira), Ursus (headed by Foreteller Aced), Leopardus (headed by Foreteller Gula), Anguis (headed by Foreteller Invi), and Vulpes (headed by Foreteller Ava). The Foretellers were master Keyblade wielders and occasionally offered guidance to their followers, but largely left them to manage themselves while the Foretellers did their own work.
The Foretellers taught that the world is divided into light and darkness, with light being good and dark being evil. By succumbing to feelings of fear, inadequacy, envy, paranoia, or other negative emotions, a keyblade wielder threatened to lose their hearts to darkness. The only thing that could be done at that point would be to kill them before they could turn into a monster and hurt others. Fear that one of the Foretellers might be such a person led the Foretellers to clash, with the paranoia creeping down into their followers. Thus, the Keyblade War occurred. The Foretellers disappeared afterward.
While Unions were forbidden from working with one another, there were individual members that befriended one another. Some of these relationships were broken by the increasing paranoia of the Foretellers; others survived.