The BattleTech universe is a diverse place, spanning more than a millenium of history and several thousand light years of space. From the nation states of the 20th century up to the Republic of the Sphere of the 32nd century, Battletech spans myriads of places and trillions of people. Interstellar, succession and civil wars, fragmentation and infighting gave birth to countless factions, of which most are noted below.
 Regions of Space
 Inner Sphere
The Inner Sphere is the heart of the Battletech Universe. Centered around Terra, it stretches across roughly 500 light years in all directions. The most consolidated of all interstellar regions, the Inner Sphere is dominated by five Great Houses.
|Factions in the Inner Sphere|
|Inner Sphere States||Republican Splinter States||FWL Splinter States||Inner Sphere Clans|
|Capellan Confederation||Bannson's Raiders||Duchy of Tamarind-Abbey||Clan Hell's Horses|
|ComStar||Dragon's Fury||Marik-Stewart Commonwealth||Clan Jade Falcon|
|Draconis Combine||Spirit Cats||Oriente Protectorate||Clan Sea Fox|
|Federated Suns||Steel Wolves||Regulan Fiefs||Clan Wolf|
|Lyran Commonwealth||Stormhammers||Rasalhague Dominion|
|Free Worlds League||Tall Trees Union||Raven Alliance|
The Periphery refers to the region of space immediatly surrounding the Inner Sphere. The border between Periphery and Inner Sphere is generally 450 - 550 light years away from Terra. The Periphery is surrounded by the Deep Periphery, though the borders for this region of space are more nebulous. The Periphery is littered with small colonies and a handful of interstellar nations. 
|Factions in the Periphery|
|Calderon Protectorate||Lothian League||Rim Collection||Tortuga Dominions|
|Filtvelt Coalition||Magistracy of Canopus||Rim Territories|
|Fronc Reaches||Marian Hegemony||The Barrens|
 Deep Periphery
Deep Periphery refers to the depths of unexplored space and/or human colonized space located beyond the (known) coherent human sphere of influence, namely the Inner Sphere and the adjacent Periphery realms. Due to the vague nature of the term "Deep Periphery", there is no clearly defined beginning nor are there any boundaries. 
|Factions in the Deep Periphery|
|Chainelane Isles||Hanseatic League||Umayyad Caliphate|
 Clan Homeworlds
The Clans were originally the self-exiled remnants of the Star League Defense Forces. Travelling 2000 light years corewards, they colonised several worlds in the Kerensky cluster. The exiles evolved into a warrior-based civilization that would sweep through the Inner Sphere like a whirlwind 250 years later.  The current factions in the Clan Homeworld are unknown.
 Historical Factions
 Early Spaceflight
Between the mid-20th and the early 22nd century, Terra began a long process of political unification, first into the Western, then the Terran Alliance. At the same time, developement of a practical Fusion Engine allowed for the first off-world colonies, on Luna, Mars, and Venus. 
|Factions during the Early Spaceflight Era|
|Western Alliance||Asian Co-Prosperity Sphere||Terran Alliance|
 First Exodus
After the success of the Deimos Project, the era of the First Exodus was one of rapid expansion and colonisation - both sanctioned settlers and dissidents fleeing the increasingly repressive Terran Alliance had established 600 known colonies by 2235. The Outer Reaches Rebellion ended the First Exodus, as the Terran Alliance completely withdrew from its colonies. 
|Factions during the First Exodus|
|Inner Sphere||Deep Periphery|
|Chesterton Trade League|
 Second Exodus
Due to the power vacuum of the Alliance's withdrawal, chaos and warfare broke out. Many colony worlds were no longer sustainable or subject to prolonged conflicts, their inhabitants again took to the stars, spreading even beyond the settlement boundary of the First Exodus. Meanwhile, the first true interstellar states formed, fought and absorbed each other until the Inner Sphere consolidated into an armed standoff between the six Great Houses.
 Age of War
The Age of War began in 2398, when the Houses Liao and Marik fought over Andurien. Initial savagery was eventually followed by the ratification of the Ares Convention, a set of guidelines which made war much less brutal, but also a near constant occurrence. Thanks to the Terran Hegemony's Strategy of Aggressive Peacemaking, the Age of War ended with the signation of the Star League treaties by the six Great Houses.
|Factions during the Age of War|
|Inner Sphere (Major)||Inner Sphere (Minor)||Periphery||Deep Periphery|
|Capellan Confederation||Principality of Rasalhague||Illyrian Palatinate||Alfirk|
|Draconis Combine||United Hindu Collective||Magistracy of Canopus||Axumite Providence|
|Federated Suns||Outworlds Alliance||JàrnFòlk|
|Free Worlds League||Rim Worlds Republic||Nueva Castile|
|Lyran Commonwealth||Taurian Concordat||Virginian Union|
 Star League Era
Formally unifying the Member States of the Inner Sphere in 2571 and officially subjugating the Territorial States of the Periphery in 2597, the Star League Era was one of overt peace and hidden wars. Later called a Golden Age by many, the Star League allowed for peace, prosperty, and significant technology progress. Weakened by a string of bad rulers, hidden wars, and unrest in the Territorial States, the Star League eventually collapsed after the Amaris Civil War.
|Factions during the Star League Era|
|Inner Sphere||Periphery||Deep Periphery|
|Capellan Confederation||Circinus Federation||Alexandrian Covenant|
|Draconis Combine||Illyrian Palatinate||Alfirk|
|Federated Suns||Magistracy of Canopus||Axumite Providence|
|Free Worlds League||Outworlds Alliance||JàrnFòlk|
|Lyran Commonwealth||Rim Worlds Republic||New Delphi Compact|
|Star League||Taurian Concordat||Nueva Castile|
|Terran Hegemony||Tortuga Dominions|
 Golden Century
After the fall of the Star League, Operation Exodus of the Star League Defense Forces led them into the Kerensky cluster, where they settled down. After falling into civil war and a second Operation Exodus, the remaining loyalist SLDF forces reorganised themselves into the Clans and retook the war-stricken worlds. The Golden Century was the following period filled with unprecedented growth, technological progress, and a maturation of each Clan's individual self identity. 
|Factions during the Golden Century|
|Crusader Clans||Warden Clans||Abolished Clans|
|Clan Blood Spirit||Clan Cloud Cobra||Clan Burrock|
|Clan Fire Mandrill||Clan Coyote||Clan Mongoose|
|Clan Hell's Horses||Clan Ghost Bear||Clan Widowmaker|
|Clan Ice Hellion||Clan Goliath Scorpion||Clan Wolverine|
|Clan Jade Falcon||Clan Nova Cat|
|Clan Smoke Jaguar||Clan Sea Fox|
|Clan Star Adder||Clan Snow Raven|
|Clan Steel Viper|
 Succession Wars
After the collapse of the Star League and the exodus of the SLDF, the five remaining Great Houses - after dividing the remaining Terran Hegemony among each other - began a series of brutal wars to claim the position of First Lord. The first two Succession Wars, apocalyptic conflicts encompassing the entire Inner Sphere, brought technological knowledge down to levels last seen on pre-spaceflight Terra, and only the establishment of ComStar on independant Terra prevented a total collapse of interstellar communication. The Third Succession War became an endless downward grind, led by neo-feudalistic Mechwarrior families and covertly helped along by the increasingly corrupt ComStar. It was only the Fourth Succession War that brought a fragile peace and a new status quo to the Inner Sphere - the victorious powers of the Federated Commonwealth (at the time merely an alliance between Federated Suns and Lyran Commonwealth) against the Concord of Kapteyn of Free Worlds League, Capellan Confederation, and Draconis Combine.
 Clan Invasion
After almost 3 centuries in exile, the Clans returned to the Inner Sphere in a coordinated drive towards Terra until losing a trial on the planet Tukayyid, agreeing to a 15 year long truce. With the Clan threat temporarily eliminated, the Great Houses went back to fighting each other - the barely established Federated Commonwealth broke apart again, the Word of Blake led an Exodus out of ComStar, and an entire region of space descended into anarchy. When the hastily established Second Star League managed to destroy Clan Smoke Jaguar during the Refusal War, the Clan invasion was finally over, but the problems in the Inner Sphere were only beginning to escalate.
 Civil War Era
Nominally a civil war between the two halves of the sundered Federated Commonwealth, the Civil War quickly degenerated into a conflict involving all major Inner Sphere powers, an uncounted number of mercenary units, and several of the relocated Clans. At the end of the conflict, the Federated Commonwealth was gone forever, with the Federated Suns and the Lyran Commonwealth being recreated by their new rulers.
The Word of Blake Jihad began as an impulsive reaction by the Word of Blake after the fall of the Second Star League in 3067. It eventually escalated into a series of conflicts between most major Inner Sphere and Periphery factions, leaving several realms (last among them the Word of Blake itself) utterly destroyed. United in a fragile coalition, the Anti-WoB forces eventually forced the Word back unto Terra itself, which was finally reclaimed in 3078. 
 Republic Era
 Dark Age Era
Modern mercenaries have their root in the chaos of the Second Exodus, when they were commonly used in the hundreds of border conflicts between the emerging statelets. In use during the hidden wars of the Star League members, mercenary units began to multiply in numbers and power since the beginning of the Succession Wars. Even in later eras, mercenaries retain their prominent role in military conflicts.
|Other notable factions|
|Cult of the Saints Cameron||Interstellar Expeditions||Brotherhood of Cincinnatus|
|Far Lookers||Irian Technologies||Davion Warrior Cabal|
|Inheritors||Sixth of June|
|One Star Faith|
- ↑ 1.0 1.1 The Periphery (2nd edition), p. 6
- ↑ Explorer Corps, p. 13
- ↑ 3.0 3.1 Invading Clans, pp. 16, 84, 108, 133-134
- ↑ DropShips and JumpShips, pp. 5-8
- ↑ The Periphery (sourcebook), pp. 12-14
- ↑ The Periphery (sourcebook), pp. 14-19
- ↑ Star League, pp. 28-35
- ↑ Star League, pp. 37-98
- ↑ Shattered Sphere, pp. 7-8
- ↑ FedCom Civil War, pp. 13-16
- ↑ FedCom Civil War, pp. 180
- ↑ Jihad Hot Spots: Terra, p. 130
- ↑ Catalyst Game Labs' forum: "Topic: The Republic era?"
- ↑ Catalyst Game Labs' forum: "Topic: The Republic era?"
- ↑ Field Manual: Mercenaries, pp. 7-9