Carcosa

Carcosa, the Lost Isle, is a burgeoning demi-realm believed to be hidden within the Nullfoam that is the primary home to the Carcosan, or Dissian, people. It is said to be impossible for any fully sane man to find and impossible for any fully sane man to survive for long in, with much of the anarchy in its streets being open to the Null itself. Bedecked in impossible geometries and larger than would ever be possible for a single city in realspace, it’s theorized to be the culmination of interconnected nodes hidden away in the labyrinthine voidpaths, themselves the work of the mad followers of the first gods. Viewed in this way, it’s less a city and more a constellation of settlements woven amid the in-between of realities.

There are powers in the Lost Isle, certainly, though none entirely concrete. The Triad, once a criminal syndicate on a now-dead world, lives on as originating framework for The Isle's Diabolic Congress - a loose parliamentary body that serves to reign in the interests of Carcosa's multitude of power figures - typically titled Diabol or Archdiabols, with the exception of certain minorities such as the Rabbi of Temple Ward and Dean of the College of Hermetic Esoterica. Notably, the Diabolic Congress exercises no authority over the general populace of Carcosa, solely those Diabols who are admitted into it.

Pre-Oksidan Crusader era
Having become "lost" twice, Carcosa's earliest known history was that of its original inhabitants, the Yith, before they were displaced by the Ekhanoi, also known as the Dark Elves, who were in turn conquered by the cosmic entity known as The King in Yellow, itself likely an avatar of Nyarlathotep. Of the Yith's presence on Carcosa, extremely little is known, their presence only evidenced by their tombs, occasional placenames, and artifacts. Little is known of the Ekhanoi prior to their subjugation by The King in Yellow, with there being no firm theories as to why they conquered the Yith or their home prior to invading The Isle.

Carcosa's well understood history begins with its invasion and conquest by the Oksidan Crusaders in [time]. Though ultimately successful, the early stages of the invasion were an abysmal failure - resulting in staggering losses for the Oksidan Crusaders before a suicide-assassination of the King in Yellow by Nanuq of Oksida resulted in the collapse of the Ekhanoi - King in Yellow forces and the crashing of the Carcosan demiplane into that of Provenance. Following this, an interim period began wherein various factions arose within the Isle without any formal organization or policy backing, resulting in a disjointed anarchy reigning over The Isle for much of its time on Provenance.

Provenance era
Though there as a brief attempt by power figures within the Oksidan Crusaders such as Nanuq of Oksida prior to her death and Harkad avStygia to assert Oksidan Syndicalism over Carcosa, the losses suffered by the Oksidan Crusaders, the sudden assimilation of the Ekhanoi, and the ambitions of Dissian figures such as Nanuq's daughter Cinna saw to the effort's failure. The result was a disjointed amalgam of factions with varying alliances that saw The Isle blossom as a haven for criminal elements, dissidents, and oppressed minorities from elsewhere on Provenance.