Shadow Earth was created in the early 1500's. The Black Death and the Spanish Inquisition decemated Paranormal populations to a point that if something hadn't been done, they'd become extinct.
The leaders of each race gathered in what is now known as the Lern Symposium to discuss and debate the future of the Paranomal Races. It was decided to create an alternate earth; a Shadow earth, where the races could live and rebuild their populations.
A spell was crafted by the most learned of the Paranomals, so complex that it required all members of each race to contribute energy to power the spell. This spell needs to be renewed every 50 years, during the Festival of Lern.
After Shadow Earth was created, the leaders decided the spell could easily cause trouble if anyone had access to it. To safeguard the spell, it was broken into five pieces and bound in the Forbidden Tomes of Magic and stored in the highest level of security the group could devise.