This isn't my first essay on how the Sublight universe is put together. But the concepts for all three regimes has evolved as I've tried to tell the story. This is my latest update on who the three factions are.
I'm going to simplify the history of my Universe ever so slightly. Historical periods in the past century will be as follows:
The Pre-Tegic world is mainly like the world we have to day. Some historical events differ. But their world and our world were the same world prior to September 11, 1777.
A gilded age where the discovery of Tegic changed society, and caused the rise of several competing empires around the world. People look back at this period as "the good old days".
The empires fueled by Tegic go to war with one another. The result is an increasingly brutal conflict that escalates with every new discovery of ways of destroying.
A period of darkness, destruction, or, at the very least, economic turndown. Most of the livable areas on Earth are contaminated after decades of Tegical warfare. Early in the Cataclysm, anyone with the means escaped to new colonies on the Moon. By 1948, much of the pollution was cleaned up, and people began emerging from their shelters.
The development of fusion propulsion started a renesance of space development. Nations on Earth who never could sustain a space program began to look at the Asteroid belt to expand. While the immense power of fusion is making cleanup after the Cataclysm possible, a movement starts to evacuate the Earth. Humans will continue their development in the Stars, leaving mother Earth to heal her wounds.
The settlements on the Moon, by this point in time, were consolidated by force under the Banner of Krasnovia, following a series of worker rebellions. The former elites of Luna escape to form their own fiefdoms in the Asteroid belt and earth-crossing objects.
The Circle Trigon formed as a means to mediate disputes between the powerful houses of the Inner System. It's a mafia like system that establishes an order out of the chaos. Theft and conquest are formalized. Non-violent means of establishing disputes are established using magical sports.
Back on Earth, Krasnovia was not interested in absorbing throngs of new immigrants. The Circle Trigon was only interested in exploiting any newcomers. So the nations that remained banded together to form the Internation Space Treaty Organization (ISTO). The ISTO would allow all of the smaller nations to band together to build larger capital investments than any one nation could pull off on their own. This massive investment in space construction would need a fleet of ships to defend it from the Raiders and from the increasingly hostile Krasnovia.
For Krasnovia's part, they viewed the emergence of a new superpower as a threat. They began a massive shipbuilding program. While they had plenty of resources on the Moon, a new nation forming in the Asteroid belt could cordon them in. They started trying to stake claims over all of the choice places to settle in the Solar System.
For ISTO's part, Krasnovia's aggression to their aggression caused them to redouble their own efforts to build a fleet. This led to a massive arms race.
In 1962, Krasnovia enjoyed a temporary advantage in tactical strength. ISTO was months from launching several new powerful warships. A new shipyard under construction on the planetoid Psyche was threatening to dwarf even Krasnovia's industrial capacity. The military decided it was now or never to stop ISTO before it grew out of control.
Most of ISTO's fleet was destroyed in the opening hours of the War. They were moored at stations near Earth. Krasnovia's fleet then set out from Luna to Psyche to destroy the shipyard facilties. But because their ships were a mix of fusion and pre-fusion craft, the fleet deployment was a mess. As they approached Psyche (who had weeks of notice they were coming) laid the entire Krasnovian fleet to waste with stand-off missiles.
This utterly unsatisfying outcome led both sides to sue for peace. The negotions that followed led to the Treaty of Reykjavík. In this treaty, the two sides carved up the Solar system, leaving "neutral" and regions that neither side enjoyed an advantage over, or that were already dominated by the Circle Trigon.
Of course, the Circle Trigon, not having been part of any of these negotiations, doesn't feel obligated to honor any of the terms. They do enjoy the relative peace and stability it brings. However, several kingdoms in the Asteroid belt now fall under ISTO jurisdiction. This has led to a complicated mess where some colonies are both ISTO and Circle Trigon.
For ISTO's part, they are just as happy that those regions continue to operate on their own. However, when pirates from one of these contested worlds nails a Krasnovian convoy its a complete dumpster fire for diplomacy.
For Krasnovia's part, they love to fund and arm insurgencies to keep the ISTO too distracted to represent any kind of real threat for their own ambitions.
While the treaty of Reykjavík has kept Krasnovia and ISTO from fighting each other, there is still an arms race going on in the background. Each side was allocated an equal number of hulls for each class of vessel. Krasnovia rebuilt their fleet to fill their entire quota in short order. ISTO took longer to rebuild, but the ships they construct are all dual purpose. It's so egregious that their battle carriers and their "mobile deep space settlements" share the same hull numbering system. (Even numbered hulls are battle carriers, odd numbers are MDSS's) The MDSS series uses all of the same engineering systems as the battle carriers. In fact, an MDSS can even support an even larger number of embarked strike craft and smaller capital ships. They just lack any offense armaments. (That mass, volume, and power consumption is replaced with ore processing and fuel refineries).