In all simple form it goes like this.
600AS + - Explorers find a system rich in resources, mining colony starts
650-725AS - Crossbones were small band of hit for hire; Refugee War at the mining facitiy that is now called "Sunken City." After the war the sirius side jh collaspes
700AS - Foundation hire Crossbones as personal military
750AS- Foundation starts becoming violent and taking over smaller government roles
800AS- Crossbones and the Foundation fuse into one. Starts many terrorists attacks
816AS- Gothera's, the leader of the CBF, brother commits the largest terrorist attack ever attempted by the Foundation, with success
818AS- Crossbones Foundation secures several fleets. Rockefeller plots to remove Gothera from power, Gothera plans to kill Rockefeller for his own entertainment
819AS- Crossbones conduct first of three military operations before invading Gallia to search for the "Sunken City."
820AS- Crossbones skim the edges of Gallia in open conflict.
825AS or so- Crossbones manage to locate the host system of the Sunken City
825-27AS - Octavian War, where the Crossbones and Octavian Nationalist fight for control. Three way battle between Gothera's Crossbones, Rockefeller's Fleet, and Octavian Nationalist.
827AS - Zuel Calender created to celebrate the victory over Gothera's Crossbones The year starts 001ZC; remaining Crossbones "converted" and called themselves Octavian Royal Forces.
004ZC (830AS); Nation of Octan contacts the remaining population in Sirius.