The League of Nobles was a confederacy of 10,000 free human systems that survived the Time of Titans and the rise of Omnius, and resisted the thinking machines for several millennia until Omnius' defeat at the Battle of Corrin.
After the emergence of the Titans in 1287 BG, the 10'000 systems of the Old Empire that did not fall prey to their AI network infiltration banded together for mutual protection against their new enemy.
When a man called Bovko Manresa settled on then isolated Salusa Secundus his mansion had become a meeting hall for refugee humans; the League supposedly was formed out of these meetings and Manresa was the first Viceroy.
After the death of Serena Butler's son Manion, the war between the two sides escalated. The League formed the Army of the Jihad to combat the forces of Omnius. This change also saw the League of Nobles become more centralized, with the primary world of Salusa Secundus taking further control of all League foreign and military policy.
The Omnius Scourge was a significant hit by Omnius during the latest stages of the War. Before its suppression the virus had taken approximately half of the League population. By 88 BG the League Worlds had barely 2/3 of their former populations. Many noble lines had been wiped out, and new centers of power began to emerge as ambitious survivors gathered their own empires, declaring themselves a fresh branch of the noble tree and claiming rights and privileges.
Families were encouraged to have many children, but a sufficient workforce to sustain previous levels of agriculture and industry did not exist. Everyone had to work twice as hard as before.
After the destruction of Omnius Prime at the Battle of Corrin the League evolved into the new Imperium, led by the Butler family under their new name of House Corrino. Probably the League was reestablished as the Landsraad.
The League had several internal and diplomatic matters to resolve such as the relationship to the Unallied Planets. The Buddislamics of the Unallied Planets shunned the League as infidels. However the League thought that if those worlds expressed their support or joined the League, it would much benefit both. One of the internal controversies the politics faced was the view on slavery, which was embraced on Poritrin and Zanbar, who employed Buddislamics as slaves.