Covenant Separatists is the name given to the forces who broke away from the Covenant during the Great Schism, composed of all the ejected Sangheili, as well as others who allied with them. When the Great Schism broke out on November 3 2552, the entirety of the Sangheili species were forced out of the Covenant. The High Prophet of Truth had ordered the Covenant military, now led by the Jiralhanae, to massacare the Sangheili. This caused a massive civil war to erupt across Covenant-controlled space.
Though only the Sangheili were forced out, many of their former allies sided with them rather than the Jiralhanae and the San'Shyuum, such as many Unggoy and Mgalekgolo and even one prophet, Zo Resken.
Within the Covenant Separatists, only the Fleet of Retribution allied with humanity during the final battles of the war.
After the Covenant Sepratists were victorious in destroying the Covenant that had betrayed them, the ejected Sangheili split off into several different factions. The Sangheili who were in the Fleet of Retribution would later form a faction known as the Swords of Sanghelios, which would become the official government of Sanghelios.