Approximately 250 BD there was not only a volcanic type eruption but a magical experience and explosion. This even changed the topography of the island from having one large mountain to having four mountains. One each to the North, East, South, and West. This also left a sizable crater where the single mountain once stood. The landscape changed also; what places were once on the island where wiped clean off the map. Some where never seen again, some left in ruins. With this being a physical and magical event, the inhabitants were scattered all over the outer area of the island. All beings and races where scattered with no rhyme or reason to the outer areas of the island. If there was a family of four alive on that day, the father could have very well been burned to ash from the volcanic eruption, the mother somehow magically protected and transported to some part of the island, while the children could have been teleported together or separately. Or it could have been any combination as a child was turned to ash, the father protected from harm and transported, the mother and other child teleported to two different places on the island. There is no known rhyme, reason, or explanation for who died, who lived, or why (if they lived) they were transferred where they were.
After this event, the inhabitants found that they could no longer leave the island. No new ships arrived to the island and any ships that sailed too far from the island, either were never heard from again, or they found that they could not get away from the island. Something would keep them in range of the island. Ships can get about 20-30 miles off the coast. Along with this, magic users and beings that that could travel to other planes, found that no matter what they tried they could not travel to the same plane of existence the island was on without traveling back to the island. If they tried to travel to the main land or some other continent within the same plane as the island, they always would end up back on the island. No one has been able to explain why or how.
The Great Decimation ultimately lead to a rift within the island and it became two sided, good vs evil.