The Clans are a civilization in the Battletech Universe. Descended from a remnant of the Star League Defense Force which fled from the Inner Sphere when the shit hit the fan and spend the next two and a half centuries developing on their own course before returning back in 3049.
In 2766 a guy named Stefan Amaris (ruler of the Rim World's Republic) launched a coup d'état after killing all known members of the Terran Hegemony's House Cameron while the majority of the SLDF was out fighting rebellions in the periphery, killing the young First Lord and seizing control of the Terran Hegemony. This started a fourteen year long civil war in which the SLDF under the command of Aleksandr Kerensky dismantled his support base and moved to liberate the Terran Hegemony in spite of being cut off from resupply and limited support by the Five Great Houses. But while he did succeed in toppling Amaris' Asshole Regime, the Star League did not survive the fall of House Cameron and fell apart shortly afterwards. In spite of internecine infighting within the Great Houses, all agreed to strip Alexandr Kerensky of his authority while secretly seeking to subvert the SLDF's individual regiments as recruits for their planned wars to claim the Star League's throne. War was on the horizon between the Great Houses but Kerensky was unwilling to seize power for himself or see his remaining army and fleet used in the looming conflict. As such he got the SLDF leadership together in secret and proposed something to save the Inner Sphere and themselves: leave the Inner Sphere and start up somewhere new. Most agreed and in 2785 a fleet loaded with millions of SLDF troops and their families (including Alex's wife Katyusha and two sons Andery and Nicholas) left the inner sphere for greener pastures.
After a long voyage through the unknown they found some uninhabited worlds beyond the Periphery known as the Pentagon Worlds. They set up shop, discharged most of their soldiers and began rebuilding to try to build a bastion of the Star League in Exile. Unfortunately some of the demobilized guys decided that they'd be better off forming their own petty kingdoms and soon enough there was a big shit fight in 2800. Aleksandr (already more than 100 years old) died. In this chaos, his son Nicholas managed to get the support of some loyal troops and most of the SLDF Fleet and made his way to another world nearby called Strana Mechty along with a number of refugees brought in later. Convinced that the current order of things and the Star League ways of thinking were fundamentally broken he decided to not only establish a new colony, but also build a new society from the ground up, dividing his warriors into twenty Clans. In 2820 the Clans returned to the Pentagon Worlds during Operation KLONDIKE, reconquering them and imposing Clan culture onto the populations of these planets.
After Nicolas's death, the system chugged along quite well with the occasional hiccup in what was known as the Golden Century. Eventually in the 2900s there was a split between two factions of The Clans: the Wardens (who felt the Clans should keep to themselves and only get involved in the Inner Sphere if it was threatend by someone else) and the Crusaders (who saw it as their duty to conquer the Inner Sphere and restore a new Clan based Star League).
Even though there is a Clan Council for settling disputes and acting as a whole, each Clan operates mostly independently of its fellows. "Peace" is not really a thing in Clan Society. When the Clans are not out conquering others, they're fighting low intensity highly ritualized wars with each other. Yet, what made the Clan Homeworlds spared the Succession Wars level of violence that sent the Inner Sphere back to the stone age was the application of Zellbrigan and the Honor Road, which emphasised individual unit and warrior prowess while minimizing collateral damage.
Clan Society is militaristic, authoritarian, honor bound and strictly hierarchical. It's mostly built around a rigid caste system in which one's role in society is typically assigned in childhood and social mobility is a rarity. The Economy of each of the Clans is largely centrally planned and mostly concerned with producing more mechs, ships, weapons and warriors.
One of the quirks of Clan Society is that most people only have a given name. More on that in a bit.
- Warrior Caste: The rulers of Clan society trained the Spartan Way. Most of them are grown in bulk in industrial exowomb factories and raised in sibling companies, but a few applicants from the general populace are let in. Many flunk out one way or another and become part of the civilian castes while many others end up dying in brutal training regimens and trials for combat. Those that become Warriors are typically hard as nails and brutal fighters. They're three main flavors of Clan Warrior: Elementals (Battletech's answer to Space Marines, huge guys and gals who wear power armor), Pilots (small fellows with big eyes and heads who can take a lot of Gs like the T'au's Air Caste) and Mech Warriors.
- Scientist Caste: Scientists, inventors, researchers and the like who expand on the Clan's knowledge base and run the eugenics programs. The second most powerful caste in Clan society who can actually overrule the warriors on certain matters.
- Technician Caste: Mechanics, engineers and spacecraft crews who keep the machinery of Clan Society humming along.
- Merchant Caste: Traders as well as managers, artists and a wide variety of other functions required to run the economy of Clan Society. They have a higher status in Clan Diamond Shark.
- Laborer Caste: The proles who do all the grunt work to keep everyone else fed, housed, equipped, armed, pooping in unclogged toilets and so forth.
- Dark Caste: Not an official caste but a bunch of outcasts which live on the edges of Clan society which makes for convenient target practice for clan warriors.
In addition each caste has it's own internal hierarchy, for example the Merchant Caste has retail clerks at the bottom and top negotiators for big inter-clan deals at the top. For warriors this is not only reflected in rising up the ranks but a Desire to win a Bloodname throught gaining honorable victory for thei clan. Having a bloodname means they get a surname and their genes will be used to produce the next batch of Warriors. Really accomplished scientists can be awarded a Labname like "Einstein" or "Darwin", but non-Scientists rarely use them.
There are originally twenty clans formed by Nicholas Kerensky but over the course of the centuries, many were destroyed or absorbed into other factions. Besides the others mentioned on the Battletech page, the most relevant ones are the ones below
- Clan Wolf: The first "Mary Sue" Clan, having the ilKhan along their ranks kinda marks you for that. Also known for fielding the Timber Wolf which plenty call a poster boy for the series. They actually won their objectives in the battle of Tukayyid.
- Clan Jade Falcon: The other "Mary Sue" Clan as when you think of honor-crazed warrior cultures that went full murder-hobo. Were the asshats that invaded MY HOME PLANET in the animated series. They earned themselves a draw on Tukayyid at about the last minute.
- Clan Diamond Shark: Once Clan Sea Fox until they saw a Diamond Shark devour a Sea Fox whole. Fitting that their fighting strength was almost wiped out in Tukayyid due to their inexperience in fighting a actual war as opposed to the dance and diddy that the Clans call a war. Current run by merchants after their warrior caste was basically butchered to the last.
- Clan Ghost Bear: Moderate fence sitters that actually attempt to do their homework on their foe? My God, it is like they have a brain... At any rate, were slow to adapt new tactics but moved in a steady pace for effect. The other Clan that got a draw on Tukayyid.
- Clan Smoke Jaguar: The Asshole Clan. They earned getting smoked on Tukayyid, bidding away a vast majority of their forces to get the first deployment and only to have them repeatedly baited into ambush after ambush on Tukayyid by being the most aggressive Clan during the invasion.