The Covenant, also referred to as the Covenant Empire or Covenant Hegemony, was a massive religious hegemony of multiple alien species that completely controlled a large portion of the Orion Arm in the Milky Way Galaxy for thousands of years. Originally a mutual alliance between the San'Shyuum and the Sangheili, the Covenant expanded to include six other species (Huragok, Mgalekgolo, Unggoy, Kig-Yar, Yanme'e, and Jiralhanae) united in the worship of the mythicized Forerunners and the Halo Array.
Ruled by the High Prophet of Truth along with High Prophets Mercy and Regret in 2525, the Covenant waged a genocidal campaign against humanity until they were defeated in December 2552. Despite being one of the most powerful military forces in the known Milky Way galaxy at the time, internal conflict combined with stubborn human resistance were formidable enough to shatter the bonds that held the empire together. This internal conflict broke the Covenant in two, forcing out the Sangheili species.
Following the Covenant empire's end at the Battle of the Citadel, a small remnant of surviving loyalists would reemerge years later, and a number of new factions were created by the fallen empire's former subject species after the conclusion of the war. Some of the separatists sought to recreate the Covenant entirely under Sangheili rule, free from San'Shyuum influence. One notable splinter faction of Sangheili self-proclaimed to be a new "Covenant" was created by Jul 'Mdama, being one of several factions which maintain some tenets of the fallen Covenant's religion. Other hostile factions that utilize assets from the former Covenant empire include Merg Vol's faction, Sali 'Nyon's faction, Vata 'Gajat's faction, the Banished and the Order of Restoration.
The Order of Restoration is currently the only faction that is still attempting to restore the Covenant, having succeeded in gathering many forces including Sangheili that left Sanghelios after Thel 'Vadam and the Swords of Sanghelios began working with the UNSC/UEG and several groups of Jiralhanae who still worship the Forerunners.