Clans

The Clans are descendants of humans that left the Inner Sphere roughly 250 years ago after the fall of the Star League to avoid the resulting Succession Wars that led to the five Great Houses becoming independent nations, as things stand in the Inner Sphere today. These people included the bulk of the Star League Defense Force, which saw no possibility of averting the coming civil war, their families, and anyone else who wanted to go with them.

The conditions on their new home were harsh. There were new diseases, and they had to build all new infrastructure. Tens of thousands died during the early years. To survive, they formed a new social structure based on a caste system and divided into clans. Each clan has its own military, scientists, civilians, etc. They implemented a eugenics program to further strengthen their population and improve their 'Mech warriors.

Since the Clans left before the Succession Wars, they never lost the Star League 'Mech technologies (and presumably other technologies not relevant to the game) that were lost within the Inner Sphere. The Inner Sphere has since regained many of them as Lostech, and is happy to even have that. On the other hand, the Clans retained and expanded upon the the ER Large Laser, LB-X 5, Ultra AC 5, and Streak SRM 2, weapons developed by the Star League, developing a full range of each. In addition, while the Inner Sphere's research has been nearly stagnant during their almost non-stop fighting, researchers among the Clans improved their weapons technology considerably. Thus even when comparing the same weapon, the Clan version is superior.

When comparing IS and Clan 'Mech technologies, the most notable Clan improvements are:
 * Clan Lasers and PPCs do more damage, have more range, and some use less space
 * Clan Autocannons weigh less and use less space
 * Clan Missile Launchers weigh less and use less space
 * Clan Double Heat Sinks use two critical slots rather than three
 * Clan electronics suites are better and weigh less
 * The Clans developed OmniMechs. However, they do still use standard BattleMechs as second line units.

Note that in MechWarrior Online, some things have been nerfed as compared with the Battletech game, in order to put Clan and Inner Sphere 'Mechs on more even footing. The overall nerf to Double Heat Sinks seems to affect Clan 'Mechs more than Inner Sphere 'Mechs, likely because their smaller Double Heat Sinks aren't of much advantage under these conditions.

Now, the stage is set for the Clans to return to the Inner Sphere and bring an end to the endless cycles of civil war, by force, and eventually re-establish a new Star League as a central government. The Clan Invasion has begun.

A much more detailed history of the Clans can be found at http://www.sarna.net/wiki/Clans.