Here it is with all of the pretty pictures pulled out, and cited. I can take it down if people think I have not given enough credit to the source.
The BattleTech Universe (heavily modified from https://www.sarna.net/wiki/BattleTech_Universe))
History In Brief
Battletech is set around the year 3025 during the Succession Wars era, a dystopic future of humanity where centuries of warfare following the demise of the once-mighty Star League has all but destroyed mankind's previous achievements. Centuries of raids and wars between major factions have destroyed the repositories of knowledge. Advanced technology is not understood anymore. Vehicles and machinery can hardly be maintained, and ritualized wars are fought over ancient spare parts and water.
Key to this is the Battlemech, a large robot built with the ability to almost mimic life due to the technology connecting them to their pilots. Battlemechs are far beyond their equivalents in more standard vehicles - the technology behind them makes them exponentially better. Their greatest limitation is that only certain individuals are able to link up with a Battlemech, the ability passed through recessive genetics. This has lead to breeding programs and focused into closely regulated aristocratic families, though it does appear almost randomly across the universe due to the genetic spread of humanity. Most aristocratic families look upon the wild card Mechwarriors as inferior, though the rarity of talent leads to their recruitment nonetheless.
• LosTech – Most technology is poorly understood at best. Intentional attacks on the major learning centers, and assassinations of key researchers, has turned an extremely difficult field to understand into something only partially understood by a very few. Factories turn out goods because they always have, and when they break, they often are repaired at a much lower efficiency. Many fabrication plants have been destroyed in combat only to never be able to restart again.
• BattleMechs: A basic premise of BattleTech is the evolution of the BattleMech as a superior war machine. Driven by human pilots with the help of neurohelmets, 'Mechs are gigantic humanoid walking tanks that imitate human movement patterns which makes them easier to control (as they can be used like super-large battlesuits) and supposedly gives them a significant advantage in mobility and versatility over other vehicles.
• Feudalism – the major factions are rules in a monarchist fashion, with most valuing MechWarrior ability, Standing Army Strength, and Wealth in that order. Might makes right in this modern Dark Age.
• Knight Errant – anyone with a Mech is automatically an aristocrat of some sort. This leads to the questing Knight feel of medieval Europe, or the Ronin of 16th century Japan. This has been embraced by most, even going so far as to cause ransoming of Mechs and Mechwarriors to be a common affair.
• DropShips: Most space traffic is handled with DropShips. Powered by fusion engines and highly efficient thrust drives, these are extremely rugged and versatile shuttlecraft ranging from anywhere between 200 to 100,000 tons in mass. They are generally easily capable of landing on planets and taking off into space again under their own power. In space, they can maintain acceleration of 1g or more for several days or weeks.
• JumpShips: JumpShips can perform jumps of up to 30 lightyears between Jump Points within mere seconds (typically from one star system to another). They are essentially Kearny-Fuchida Drive cores to which DropShips can attach themselves for faster-than-light transportation. This has allowed mankind to quickly spread to hundreds of worlds that it then terraformed. Most of these worlds turned out to be water poor, but after centuries of work they became habitable. This was the golden age of mankind, and while new flora and fauna was discovered no intelligent life has been encountered.
• Hyperpulse Generators: Known as HPGs for short, these employ the same fictional Kearny-Fuchida principles as jump drives, but instead of moving starships they transmit data at faster-than-light speed. Their range is up to around 50 lightyears, and messages are usually bundled and sent out in certain intervals (as opposed to continual transmission, which is also possible but rarely used). A communications network of HPGs was established that survived the downfall of the Star League and now marks the boundary of the Inner Sphere. The HPG network is generally associated with ComStar who exclusively operate it.
• ComStar is the last remnant of the Star League. Controlling communication towers and the last remaining Jump Ships (Hyperspace travel capable spacecraft), ComStar is a religious order worshiping the decaying remains of the Old Way. Every major location is protected by well maintained Battlemechs, leading to rumors that they have access to old unlooted armories. Or it could be that they simply control all trade between star systems with their Jump Ship fleet, and travel is not cheap.
The sundering of the Star League, followed by centuries of Succession Wars, brought about five large nations known as the Successor States. These are feudal realms, modeled after stereotypical cultural templates. They collectively comprise the Inner Sphere. Numerous other factions came and went over the course of the perpetual conflicts. The most notable and long-standing BT factions are:
• Federated Suns
The Federated Suns — House Davion
North American/West European cultural template. Though outwardly espousing the virtues of freedom and democracy, the Federated Suns is often shown to possess a strongly militaristic bent.
• Draconis Combine
The Draconis Combine — House Kurita
Feudal/medieval Japanese cultural template. Earlier sources typically depicted the Combine’s honor-based samurai culture as single-minded, cruel, merciless and often irrational; the realm remains somewhat xenophobic and aggressive.
• Lyran Commonwealth
The Lyran Commonwealth — House Steiner
German/West European cultural template. Economic powerhouse with a strong but sluggish military. Bureaucracy, inflexibility and a lack of military skill prevents them from successfully campaigning abroad, but their defenses are strong and their traders are active everywhere.
• Free Worlds League
The Free Worlds League — House Marik
East European cultural template. More a loose coalition of highly distinct minor states than a unified realm. The limited powers of the state leader versus the parliament render the League largely incapacitated and suffering from frequent infighting. A political minefield of treachery, deceit, violent uprisings, and outright revolt.
• Capellan Confederation
The Capellan Confederation — House Liao
Communist Chinese/Soviet Union cultural template. A vain state of relatively few worlds but with a large population, weakened from a long string of military defeats and territory losses. Relies on scheming and secret operations. Cunning and dangerous, but hamstrung by paranoia.
This quasi-religious sect evolved out of the Star League's Communications Ministry under Jerome Blake. Controlling all interstellar communication and acting as a supranational arbitrator, mediator and banking house, they regard themselves as the saviors of humanity and keepers of lost technology.
• The Periphery
Beyond the Inner Sphere, on the fringes of the HPG network, lies the Periphery, a lawless region that has descended into barbarism. Numerous minor realms and pirate bands exist here.
In addition to the aforementioned factions, mercenary units play an important role. Some prominent units have achieved considerable fame and power, to the point of ruling entire planets. They are effectively autonomous political entities.