The Levantine Brotherhood of Assassins, also known as Hashashin or Assassyun, was the Guild of Assassins located within the Levant, and the leading branch of the Order during the Crusades.
Under Hassan-i Sabbāh's leadership, the Levantine Assassins founded their own sovereign state in 1090, resulting in the first historical records of the Assassins' existence and the Order's entering into public consciousness. Accordingly, the Levantine Brotherhood was a far more recognized organization than the other Assassin branches. Not long thereafter, their sworn enemies followed suit by rechristening themselves from the Order of the Ancients to the Knights Templar, masquerading as a military order for the defense of Christian pilgrims.
During Hassan the Younger's tenure, the Levantine Brotherhood expanded from northern Persia into the Levant when a force under the Assassin Al Mualim was sent out to establish castles in the An-Nusayriyah Mountains, most notably Masyaf. From then on, Masyaf served as one of the Levantine Assassins' principle bases, more or less autonomous from Alamut. Their feared presence in the region attracted multiple invasions by Saracens and Crusaders alike, which all proved futile, and the state played a pivotal role in the Third Crusade, exerting much political influence through its assassination of key figures.
In that conflict, Al Mualim betrayed the Order by colluding with the Templars to seize the Apple of Eden, having come to agree that a New World Order was the only solution for global peace. With the Apple in hand, he then turned on his Templar allies by having his best agent, Altaïr Ibn-La'Ahad, eliminate them one after another, but would ultimately be slain by Altaïr when his treachery was exposed.
The torch thereafter passed to Altaïr, under whose leadership the Assassin Order was reformed, with new techniques created and archaic rules and customs undone. Using knowledge gained from the Apple of Eden, the Levantine Brotherhood spread its teachings and influence across the world in an effort to make the Assassin Order a global organization, with the Levantine Assassins thus becoming the forbearers to many other Assassin branches in the process. *sorry the only thing i could find is from the assassins creed wiki - poggy*