Humanity's colonization into space was still young when the first Great Houses began to form. The Houses vied for control of space until the armies of Terra (Earth) conquered and unified them under the banner of the Star League. For a time, mankind began to advance beyond all expectation, achieving a golden age for human achievement.
This renaissance was cut short as the Star League succumbed to treachery and corruption. As the League ripped itself apart in civil war, what remained of its considerable armies fled to deep space to forge a new destiny. The Great Houses, now left unchecked, have embroiled the Inner Sphere in constant war for centuries.
Led by General Aleksandr Kerensky, the remnants of the Star League Defense Forces escaped the collapse of the Star League by fleeing to a series of remote worlds far from Inner Sphere. Genetic alteration and a descent into a warlike caste system soon transformed the former SLDF into the ferocious Clans.
The Clans consider those born with genetic enhancements as "Trueborn", and despise naturally-born "Freebirth". In the darkness of deep space they waited for their chance to attack the Successor States and resurrect the Star League.
Despite their seemingly singular purpose of claiming control over Terra the Clans are subject to their own old rivalries, which complicate the invasion plans as the Clans are divided along two conflicting ideologies: the Crusaders and the Wardens.
- Crusaders believe it is the destiny of the Clans to conquer the Inner Sphere, thereby saving it from the chaotic nature of the Successor States.
- The Wardens were initially opposed to the force invasion and consider themselves stewards of the Inner Sphere whose duty it is to protect its inhabitants.
Throughout the centuries the Wardens had been successful in staving off the Crusader invasion plans. However, the arrival of an Inner Sphere surveillance probe into Clan space gave the Crusaders the political leverage to finally begin their conquest. Numerous Warden and Crusader Clans exist within the Clan Homeworlds, but only the four mightiest earned the right to invade.