From triwiki
A few thousand years ago...
A great war between Big Sister and The Council of Magi breaks out, breaking the world apart and sending the three major continents spiraling off into space. TRI is now a flat planet, with a massive ocean surrounding the three continents, and a great Raging river separating them.
Big Sister and The Council of Magi calculate the energy and formula needed to perform a great spell to create an artificial sun and moon. The natural laws of TRI are permanently altered from this event, resulting in each continent having its own natural laws for magic and technology. Portals appear, drawing in things and people from other worlds, dimensions, and existences.