The event that brought about the rise of monstrous creatures on Storm Island was the Division. In it, the Balance between light and dark was tipped perilously off balance, causing manifestations of light and darkness to form in the physical world and fight one another for dominance, causing great destruction to all caught in between. The Shades and Aethers caused great destruction on Storm Island and forced humanity out of much of the land they once inhabited, with both sides vying for dominance of the world. The only thing that is keeping them at bay is their current conflict with one another.
The game’s plot will be influenced by this catastrophic event that has shaped the world it resides in, but will not see it being resolved but the game’s resolution. It serves as a backdrop for the action, and a reason for the enemies you face and avoid in it.