The Roiling Seas are the stretch of ocean that separate Septentionalis and Meridionalis, created by the Fracture that destroyed the Aeternum Empire. The Seas got their name from the fact that they are never truly calm. Storms, whirlpools, and tidal waves are common on the Seas and become more frequent and destructive closer to The Vortex. As such, most of the islands that are inhabited are either large enough to survive the dangers of the Seas or are far enough away from the Vortex that such nautical disasters are rarely deadly on a large scale.
At the center of each island is an intersection of magical ley lines that cover the world. Those little nexuses of power held the land around them together during the Fracture, like the roots of a tree in a great flood. The ley lines exist in every plane of existence, so even a drastic event such as the Fracture could not fully destroy these magical verticies in the material plane.
The larger islands that were further away from the Fracture’s epicenter are home to various Taifa of the Free Nations, the populations of which are largely non-humans. Some are descended from those that fled the creation Innovo Imperium during Nocte Cineris, but a majority of the populace is descended from those forced to live in the slums of Lux Citivae.
There are also many islands not within the constrains of the Free Nations, and are inhabited by strange monstrosities loosed upon the material plane by the Fracture. A few other islands house those who refused to join the Free Nations. The Upweke, as they are known, are survivors of the Fracture that were lucky enough to be near some of the weaker intersections of ley lines during the blast, which provided some protection. However, they were affected in strange and, in some cases, horrific ways by the cataclysm. Most of these islanders are extremely xenophobic and insular, so what little is known of them is largely hearsay and tall tails from sailors from the Free Nations.