History of the BattleTech universe

The Star League was a large confederation consisting of essentially the whole of humanity in the storyline for BattleTech. Founded by a treaty between the six Great Houses in 2571(note: the sixth, not on that list, was House Cameron, rulers of the Terran Hegemony and leaders of the Star League. It was annihilated in coup that caused the fall of the Star League) and lasting until Stefan Amaris' coup in 2767, the Star League was notable for ushering in a major period of relative peace and major technological advancement, consolidating the thousands of planets humanity had colonized in the previous hundreds of years.

The Star League fell in 2767, when Stefan Amaris, supposed friend of First Lord Richard Cameron, assassinated the entire Cameron family and proclaimed himself new First Lord, while the bulk of the Star League Defence Forces(SLDF), led by Aleksandr Kerensky, were fighting a campaign in the Periphery. The SLDF eventually regrouped, drove inwards, and liberated the entire Inner Sphere in a long and bloody 13-year war, culminating in the conquest of Terra. However, the SLDF, having been massively depleted in this war, no longer had the strength to hold the fractious Great Houses together, and eventually abandoned the Inner Sphere entirely in the great Exodus of the entire SLDF to the deep Periphery, not to be heard from again for three hundred years.

The five remaining great houses almost immediately embarked upon the greatest war in human history. Snatching up the rulerless planets formerly of the Terran Hegemony, and fighting each other for supremacy, the Inner Sphere devolved into the First Succession War. The fires of this war wreaked havoc on human civilization, and lowered the technology level of the Inner Sphere drastically, as well as resulteing in hundreds of millions, possibly billions, of dead. Eventually, the First Succession War ended in an exhausted stalemate after 35 years of war, only to resume in the Second Succession War less than a decade later. The Second War lasted another 34 years, further destroying the now-irreplacable base of Star League technology, and resumed in the Third War a mere two years later. The Third War lasted for over 150 more years, on and off, and by the end of the Third War in 3025, any remaining vestiges of the Star League in the Inner Sphere were merely dust on the winds of history.

However, that is not the complete story of the Star League. Following the Clan invasion of 3050, the successor states, unified by the new external threat, once again came together to form a new Star League. While its new incarnation is significantly less unified than the original(the most notable reason for this being that the position of First Lord is re-chosen annually instead of being permanently held by one family), it has proven itself on the field of battle against the Clans, annihilating Clan Smoke Jaguar in 3058. Wher the new Star League will go in future has yet to be seen, but it will almost certainly be a major force in human history, like the original.

(Author's note: I know nothing of the plotline after the end of the FedCom Civil War, so if anything thereafter contradicts my last paragraph, sorry.)