A lot has been going on behind the scenes - some art, lots of discussion, and way too much Playstation (when I should be writing). So, as things evolve, its time to recount where the setting stands (I am doing this to loud, angry music... so this might be a little aggressive): Sorry in advance, this is going to be a wall of text....
Mars (the Martian Democratic Polity): The titular good guy. It is the largest (in terms of size) single political entity in the System. It commands a large military, a sizable economy, and a vibrant political landscape. Mars recently won its freedom from the UN and Hegemon interests and now stands as the first planet in the system, outside of Earth, that controls its own destiny. Now that things have started to settle down from the war that won its freedom, Mars has a lot of economic and political issues to contend with -- a deeply divided political system, a demagogue-to-be in a leader, an economy that must struggle to find equilibrium, and a series of hostile governments all around it. Despite it all (or maybe because of it), Still, the march of history seems to be on Mars' side.
Mars is ready to take the fight for freedom and political self-determination to the other planets. There are many throughout the System that were sympathetic to Mars' war with its Imperial Masters. Pockets of resistance sprang up as Mars and the hegemons fought, and for the most part, those resistance movements and political alliances were ruthlessly put down by the OCRI crimson helmets. However, those movements bought Mars the time and space to fight the superior forces of the Imperialists by distracted its enemies and redirecting critical resources elsewhere. Many non-Martians paid for Mars' freedom with their lives -- its time for Mars to repay its blood debt and return the favor.
Earth (a series of nation states and hegemonic alliances): Earth has been through some rough times, and emerged difficult and angry. Not long ago, the population of Earth crashed in the most devastating loss of life since the bubonic plague, leaving the planet and the people a wreck, It recovered years ago, but the demands it places on its colonies to support the people of Earth are increasingly difficult to manage. Earthers are known for being affluent and prone to excpetionalism - usually at the costs of the colonies.
Earth is not united, but it is powerful. It is a mosaic of nation states and competing interests held together by custom and procedure (in this case "procedure" refers to the UN). Many of the most powerful nations banded together into like-minded blocs to help exploit the riches of the solar system. These blocs became the Hegemons, and have been the driving force towards colonial settlement of the planets and, ultimately, the rapacious demands of the Earther economy.
Earth has no one central government, though the UN passes for something similar (but much less efficient).
Luna (The Lunar Colonial Administrative Zone): Until recently the moon was nothing more than a backwater - an industrial hell of mass drivers, stand-along servers and broadcast centers, and low-grade He3 harvesting. Luna never got the attention Mars did, and served as the forgotten stepping stone towards colonization of planets further out.
That all changed when the war with Mars erupted. Suddenly, the economic engine that made Earth function was cut off. Agricultural and industrial supplies from Mars cut off rapidly, leaving the Earth economy teetering on the brink of disaster. The conservative and risk-adverse leaders of Earth decided to play it safe, and rather than wait for the Mars crisis to settle down, they started to use Luna to fill the gap left by Mars. Its been an imperfect bootstrap effort, but it has paid significant dividends for Luna -- the up-and-comer of the System.
Luna is quietly ruled by an OCRI Colonial Administrator
Mercury (The Papal State of Mercury): Mercury is a political oddity born of a number of unlikely events. Long story short, Mercury is owned by the Vatican and administered as a holding by the Holy Catholic Church. It is the engine that powers Earth - with significant resources and installations dedicated to collecting and beaming solar and fission energy to Earth where it is recovered and utilized. Mercury is also the hub for the small, lucrative, but heavily regulated trade in antimatter.
Oh yeah, Mercury also has evidence of extraterrestrial life. The Church has thus far taken a hands-off approach to the research of the fossilized extraterrestrial life, but that may not last.
Luna is managed by a Vatican-appointed Cardinal that is quietly supported by a pro-Hegemon mercantile cartel. It is formally an OCRI colony.
Saturn (The Saturn Colonial Administrative Zone) : Saturn is the home of the avant garde of the Solar System. Once in competition with Jupiter for the lead in the volatile trade, it eventually lost out to its Jovian rival. This was for the best it turned out, since it forced the Saturnine factions to turn to alternative economic models to keep up its once robust growth. Now, Saturn is the home to the influential Commonwealth of Interstellar Interests (see below) and the home of a number of powerful SCEs that push the boundaries of science and economics. If it can turn a credit, its probably happening on Saturn -- with alarming little regulation or oversight even on the most dangerous projects.
Saturn isn't a single political entity outside of the dominant Commonwealth government. Saturnine space is populated by dispersed habitats, homesteads, and moon settlements - the largest of which, Titan, is the defacto capital of the planet (and home to the Commonwealth).
Saturn has an OCRI-sponsored Colonial Administrator, but he has little real power.
Jupiter (The Jupiter Protectorate): A confusing collection of petty kingdoms and isolationist communities. Jupiter's settlement is actually nowhere near the planet, with all the habitats clustering around the Trojan, Hildans, and Greek asteroid clusters (conforming to the stable Lagrange points). This makes "Jupiter" the most dispersed of the polities in the System.
Jupiter was, at one point, the center of economic activity and energy production - back when chemical rockets were the primary mode of transportation Those heydays are gone, however, and now Jupiter plays host to those communities that either could not leave, or did not want to. The most notable exception to this is the large Jewish diaspora habs in the Hildas - serving as the new Israel since Israel proper was destroyed in a nuclear exchange with Iran in the Mid-21st C.
Jupiter serves as the lesson to the rest of the System about the dangers of crossing OCRI and the Hegemons. Before the war with Mars, the skirmishes and battles between OCRI and the Hegemons with various Jovian independence factions proved the might of the Imperial governments (even if it came at a high cost).
Jupiter has a Colonial Administrator that serves as the closest thing to a central government. Many Jovian habs remain under martial law. The Jewish Hildas are very vocal in their refusal to recognize the OCRI Administrator and have not submitted to martial law.
Venus (The Venus Colonial Administrative Zone): Venus is complicit in advancing the Imperialist agenda. The planet is ruled by the iron first of its Colonial Administrator, a woman known to have committed significant human rights abuses upon her own people. Venus is a active opponent of Mars, to the point where Venus hosts the recently ousted Martian interim President.
Venus and its administrator gets away with its horribly oppressive and eccentric government (even in the eyes of many Earthers) because it is happily raped by Colonial interests. Workers rights rarely get in the way of profits - and with corruption at an all time high, anyone with interests in Venus is getting paid handsomely. Thus far, the opponents of the Venusian administrator have yet to get the needed traction to overcome Venus' economic inertia.
That may all change, however. Two nomadic dwarf planets, nicknamed the Huns, are transiting into the inner system. They were originally thought to travel wide of any of the planets - with the biggest disruption being to the tidal movements of Earth's and Mars' oceans. The estimations were wrong, and the Huns appear on a direct collision course with Venus. A massive evacuation program began once the calculations for the impact were confirmed into the 80% range. That orderly departure is quickly braking down, turning into a full fledged humanitarian crisis as many desperate Venusians clamor for space on overloaded colonial cyclers.
Ceres (The UN Administered Zone of Ceres): Ceres is under strict military control of the UNSC and OCRI. It is a mystery to much of the system with little known besides the fact that the Imperial fleet is home-ported at Ceres.
UN/OCRI (The UN Organization of Colonial Rights and Integrity): A UN body given a large budget and wide latitude to operate and administer the off-Earth colonies so that they remain stable and profitable. OCRI's mandate has steadily expanded over the years as it has become more difficult with each pasing year to manage the colonies. OCRI now manages a giant bureaucracy throughout the System and an elite military intervention force. OCRI is the default bad guy of the setting - ruthlessly opposing Mars' goals while advancing the rapacious interests of the Imperialist Hegemons.
UN/SC (The UN Security Council): The UNSC is populated by members of the Hegemons, with each Hegemonic bloc maintaining a permanent representative and also rotating on members every four years. The Security Council is the policy body for the UN Peacekeepers, a standing military force of notable size. The Peacekeepers are the equal of most Hegemonic space forces and the enforcement arm of the UN and, more generally, colonial interests. When the problem is too large for the elite forces of the OCRI Crimson Helmets to handle, the UNSC's Peacekeeper behemoth steps in.
CAID (The [Martian] Complexity Analysis and Intelligence Directorate): The very cutting edge special forces/intelligence body of the Martian government charged with forecasting the future and ensuring that future reflects Martian ideals of freedom and self determination. CAID fuses sociology, predictive economics, and fuzzy analysis to develop the policy goals of the MDP - and has its own in-house special forces units to execute the missions required to ensure Mars' safety. CAID is known colloquially on Mars as "Fatewatch." Outside of Mars it is called a thinktank for terrorists.
MIS (The [Venusian] Ministry of Internal Security): A hybrid Ministry with expansive policing and security responsibilities. It is the enforcement arm of the Administrator and legendary for its ruthless (and brutal) effectiveness - against offworders and Venusian citizens alike. MIS and its considerable military sub-ministry are major rivals to CAID and Mars.
The Commonwealth: A loose confederation of polities, nations, and corporations tied together by the mutual desire for profit. The Commonwealth is often confused for Saturn's government, and while its' HQ and many members are located in Saturn's well, it is not official government of Saturn. The Commonwealth has members throughout the System, with allies and economic fronts on every planet and moon with a notable population. Slow to act, when the Commonwealth does make a decision, everyone in the System pays attention since its economic edicts and sanctions can virtually destroy their targets. Many Hegemons consider the Commonwealth a dangerous and unpredictable factor in Interplanetary politics.
Flirting with Dominion -- The Trans-Oceanic Republican Alliance (TORA): What was once the US, UK, Canada, Mexico, Australia, New Zealand, Ireland, Iceland/Greenland, Singapore, and Japan.
Whats Old is New -- The Ansar Community – Progressive mostly-Sunni alliance hemmed in by the irradiated wasteland that was once the holy land and a UN-puppet that plays at being Iran.
The Oldest Guard -- The European Union – They finally have a real currency and stable polity - though Iberia and France left in the 2090s.
Playing at Hegemon – The Commonwealth of Independent States (CoIS): Pretty much just Russia pretending to be a hegemonic bloc – of course, Russia is BIG (and aggressive), so it can sorta get away with it.
Direct Action – The Chinese Imperial State (ChIS): China, the Koreas, much of SE Asia and large parts of C. Asia. Corporatist and strong rivals of the ANCS.
Petite Bourgeoisie – The Africa Natal Community of States (ANCS): Violently anti-SCE. Kenya and the Congos, southward.
Sovereign Corporate Entities:
BR/BP Distributions Inc, Orbital Inc, The Access Group, Tata Lunar, Direct Intervention Ltd, Mercurial Power Inc, GrainFlowMars, Primary Source (Pvt) Ltd, Generalized Products, Deep Space Media, Saab Near Orbital, MGM/VGM Holdings, others...
The Huns: The Doom That Came To Venus.