Population Migration / Travel
Several years after the seeding it was decided that the forerunners work would be done. They organized a massive fleet of interdimensional transports. But there would be one mishap that would seal the fate of the ark and the Forerunners themselves. When they committed to the exodus they sent too many ships in too fast. It tore something of a breach between this dimension and the one they were traveling to. For the first time "Magic" as we know it was allowed to enter the world in it's magical and elemental forces. This included beings like gods, old ones, and simple spirits. Because the Ark was so close to the entry point of the Exodus, life would forever be drastically changed for everyone inside the ARK. Monsters would become commonplace, Species would harvest magic and the very beliefs of the world to use them as tools, and Celestials, Fiends, and Elementals would all be born.