Great Schism

"This is the third vector of chaos."

- Zo Resken, former Prophet of Clarity, to his Sangheili liberators

The Great Schism, also known as the Covenant Schism, or the Great Betrayal among the Sangheili, was a major civil conflict between the forces loyal to the Covenant against the Covenant separatists, which split apart on November 3, 2552. During the Schism, three major factions fought for victory: the Sangheili Fleet of Retribution allied with the UNSC; the remnants of the Covenant led by the San'Shyuum and the Jiralhanae; and the Flood, which took over the Covenant holy city of High Charity in an effort to assimilate the other warring factions. The Schism marked both the end of the Covenant and the partition of its client species for a thousand years. For UNSC, it served as a major turning point that led to the end of the war after their disastrous defeat on Reach.

Background
"Thel 'Vadamee"

For centuries over the course of the history of the Covenant, powerful Sangheili with great influence would eventually come close to discovering the truth about the Forerunners, which would falsify the Covenant religion. This was made even more apparent when Sesa 'Refumee's heretic faction spread information about the Great Journey being false. Intending to prevent the Covenant from falling apart, the High Prophet of Truth made plans to eject the Sangheili species from the hegemony, viewing them as untrustworthy and doubting their reliability and loyalty. Supreme Commander Thel 'Vadamee's failiure to prevent Demon John-117 from destroying a "Sacred Ring", was another example of a powerful and influential Sangheili commiting questionable actions, which further perpetuated distrust. Truth would eventually replace the Sangheili with the Jiralhanae, as he saw the latter as more willing and unquestioning pawns. He had appointed Tartarus, a loyal Jiralhanae, to the position of Chieftain of the Jiralhanae who would help him execute his plan. Feeding off the rivalry between the Sangheili and Jiralhanae, Truth knew that Tartarus and the Jiralhanae would be more than happy to replace the Sangheili as the Covenant's military leaders. Truth kept these schemes strictly to himself and waited until the time was right to implement them. After Truth learned the location of the human homeworld, he secretly amassed a fleet of over five hundred warships, commanded entirely by Jiralhanae, at the command-and-control station Unyielding Hierophant. In September 2552, this station and the fleet were destroyed by a group of SPARTAN-IIs who learned of its purpose shortly before the invasion could commence. This put a temporary halt to Truth's plans.

On October 20, the High Prophet of Regret made a move Truth did not expect: having discovered a significant Forerunner artifact on Earth on his own, but unaware of the fact it was humanity's homeworld, he took a fleet of fifteen ships to Earth. Immediately after Truth learned of this, he sent the remnants of the fleet he had amassed to Earth; he gave his Jiralhanae troops orders to forcibly overtake the Sangheili in command of the remaining forces on and above Earth. When Regret retreated from Earth, his Sangheili-led ships in orbit continued to engage the UNSC, but now without a leader. Only moments after, the Jiralhanae forces within the fleet and on the ground killed any remaining Sangheili, as Truth had ordered. They continued to hold New Mombasa until the reinforcements sent by Truth arrived. As High Charity and the rest of the Covenant fleet were now on their way to the newly discovered Halo Installation 05, Truth's scheme remained secret from the rest of the Covenant. Regret, who would arrive at Delta Halo weeks before High Charity and the rest of the Covenant, would serve yet another purpose for Truth: the final stage in Truth's plan. With the arrival of the commanded by Commander Miranda Keyes on Installation 05, the UNSC decided to assassinate the Prophet of Regret after they got the intel they needed, with John-117 set to carry out this task.

The Changing of the Guard
After the Prophet of Regret was killed by Spartan John-117 on November 2, 2552, the two remaining Hierarchs reorganized Covenant society. Claiming that the Sangheili could no longer protect the Prophets due to Regret's death, they replaced the Sangheili with the Jiralhanae as the Prophets' protectors. The Sangheili viewed this as a violation of the principle that the Covenant had been founded upon and threatened to resign from the High Council. This would spark the start of the Great Schism.

Conflict erupts
"The Great Schism is upon us. The unbreakable Covenant Writ of Union has been split asunder. This is the end of the Ninth, and final, Age."

- Xytan 'Jar Wattinree

Truth further demoted the Sangheili by giving command of their fleets to the Jiralhanae, including the Fleet of Profound Solitude, Fleet of Tranquil Composure and Fleet of Inner Knowledge. Truth knew that the High Council would elect a new Hierarch to replace Regret, and so he made his move to eliminate the Sangheili High Councilors to prevent a more moderate Prophet from being elected and ruining his grand plan to eliminate the Sangheili and humanity. Once enough Jiralhanae were in place, Truth instigated a pogrom by secretly ordering the assassination of many Sangheili Councilors. Many Sangheili High Councilors and former Honor Guards were ordered to meet in the Control Room of Installation 05 to begin preparing for the Great Journey. However, Jiralhanae Captain Melchus arrived at the Control Room with a large, heavily armed contingent of Jiralhanae and proceeded to massacre the Councilors and former guardsmen. Truth also freed all Jiralhanae prisoners and pardoned them after release. This was perceived as an insurrection against the Covenant to the Sangheili, as well as many Mgalekgolo and Unggoy. Loyalist factions were led to believe it was a Sangheili revolt. After the assassination of the Councilors, war broke out on High Charity, with the two sides polarizing quickly. However, this was at first a debate over orthodoxy and leadership. The true split occurred when the Sangheili discovered the truth about the Halos and the Great Journey. Their disillusionment changed their goal from reforming the purity of the Covenant to actively fighting against it the following day. Around this time, Truth left the Prophet of Mercy to die at the hands of the Flood, solidifying his place as the autocrat of the Covenant.

At the front lines of the original conflict aboard High Charity, the species of the Covenant took distinct sides. Those who followed the San'Shyuum included all but a few Jiralhanae, most Kig-Yar and Yanme'e, some Unggoy, and a minority of the Mgalekgolo. The forces allied with the Sangheili consisted of many Mgalekgolo, Unggoy and Huragok.

Chol Von, a T'vaoan shipmistress, renamed her missionary ship Joyous Discovery as Paragon at some point of the Great Schism. During the Schism, she captured a Phantom, killing two Sangheili in the process. After discovering that the Prophet of Clarity was attempting to aid the Sangheili, the Prophet of Exquisite Devotion attempted to have him executed for treason. However, a group of Sangheili led by G'torik 'Klemmee arrived and rescued the Prophet of Clarity—resulting in the death of Exquisite Devotion in the process. The group would later escape High Charity aboard a stolen supply ship, Journey's Sustenance.

Sangheili-human alliance
The shaky alliance between the Sangheili and their former foes, the humans, was forged out of necessity and revenge against the Covenant to some extent. Both sides had two common enemies that wished for their extinction: the Covenant and the Flood. This alliance of circumstance was forged in the control room of Installation 05, when Sergeant Major Avery Johnson and Arbiter Thel 'Vadamee united to prevent the Chieftain of the Jiralhanae, Tartarus, from activating Delta Halo and firing the Halo Array. The Arbiter persuaded many Sangheili—though far from all of them—to ally with the humans.

On November 17, the devastated UNSC Home Fleet attempted a last-ditch assault on the Prophet of Truth's Forerunner Dreadnought, which had integrated with the Forerunner artifact that Regret had discovered nearly a month prior. This attack failed and a Flood-controlled battlecruiser crashed in Voi only moments after Truth's fleet entered the portal generated by the artifact. However, the Sangheili Fleet of Retribution, led by Shipmaster Rtas 'Vadum, arrived in pursuit of the cruiser; as the fleet glassed the city and its environs, the Sangheili and UNSC agreed to follow Truth beyond the portal.

The Ark
The joint Sangheili-UNSC fleet arrived at the Halo Array's control center, Installation 00, on December 11. During the ensuing battle, the Fleet of Retribution completely destroyed their Jiralhanae counterpart, despite the latter's three-to-one numerical superiority. Sangheili forces later helped SPARTAN-117 disable the shield generators protecting the installation's Citadel, in which the Prophet of Truth was hiding. Master Chief John-117 and Arbiter Thel 'Vadam entered the Citadel and fought through what remained of Truth's personal guard. After reaching the control panel they discovered that the Hierarch had been infected by the Flood; as the Prophet slipped in and out of lucidity, 'Vadam stabbed him in the back. The Flood-controlled High Charity was destroyed shortly thereafter, effectively dissolving the Covenant.

Shipmaster 'Vadum evacuated the remaining Sangheili and human forces after the holy city's destruction. Seemingly, only his flagship, Shadow of Intent, remained. Any remaining Covenant forces were killed when Halo Installation 08 was activated and the Ark was severely damaged by the debris; the activation also ended the immediate threat of the Flood. The Master Chief, the Arbiter, and the AI Cortana had escaped on the frigate, which was split in half when their escape portal closed too early.

After the Human-Covenant War


Though 'Vadam sought a lasting peace with humanity, many of the Sangheili were not willing to suddenly end their war with the humans. Many Sangheili insurgents, rallied together by the Servants of the Abiding Truth, incited war against the Arbiter and his allies for collaborating with humanity. Jul 'Mdama, a former member of the Servants of the Abiding Truth, eventually formed his own revival of the Covenant, with the Sangheili again serving as its leadership caste.

With Truth dead, High Charity destroyed, and the Ark heavily damaged after Installation 08's firing, some of the remaining Jiralhanae forces tried to rebuild their tattered strength to continue their war of conquest. Even though the Jiralhanae eventually collapsed into various civil wars, they still posed enough of a threat that Sangheili commanders kept up the offensive against them for at least another six years, even as they continued to lose irreplaceable warships and the war continued with no end in sight.

2552
September 22:
 * Installation 04 is destroyed by UNSC forces. Its monitor, 343 Guilty Spark, escapes to Threshold. The Fleet of Particular Justice is damaged. The fleet's secondary flagship, the Ascendant Justice, is captured by humans.
 * A Covenant artifact retrieval team led by Sesa 'Refumee is investigating a Forerunner gas mine in Threshold's atmosphere when he encounters 343 Guilty Spark. Inspired by Spark's words, 'Refumee and his team go into open rebellion against the High Prophets of the Covenant.

October 20:
 * Thel 'Vadamee, the Supreme Commander of the Fleet of Particular Justice, is tried before the High Council and sentenced to death. However, the High Prophet of Truth overrides the Council and makes the Supreme Commander an Arbiter of the Covenant. Truth then sends him to kill Sesa 'Refumee and destroy his rebellion, which they dub "heresy".
 * Start of the Battle of Earth. The defeated High Prophet of Regret is forced to retreat to Installation 05, pursued by the.
 * Moments after Regret's withdrawal, Jiralhanae within the Covenant forces quickly kill all Sangheili and seize control of the Covenant forces on Earth under secret orders of the Prophet of Truth.
 * The Arbiter and a Special Operations Commander, Rtas 'Vadumee lead a team of Special Operations forces to Threshold, where they kill Sesa 'Refumee and successfully crush his rebellion.

October 21:
 * The Prophet of Truth's Jiralhanae-led reinforcement fleet arrives at Earth and starts the excavation of the Ark Portal. They kill all remaining Sangheili in the city.

November 2:
 * The Master Chief tracks down and kills the Prophet of Regret on Installation 05.
 * High Charity and its defense fleet arrive at Installation 05. Witnessing the assassination of the Prophet of Regret, the Prophet of Truth replaces the Covenant Honor Guard Sangheili with Jiralhanae. Insulted, the Sangheili Councilors threaten to resign from the High Council.

November 3:
 * The Arbiter and Tartarus are sent to retrieve Installation 05's activation index. The Arbiter successfully takes the index, but Tartarus tries to kill him and takes the index from him, having been secretly ordered to do so by the Prophet of Truth.
 * Most of the Sangheili Councilors are taken to the surface of Installation 05 where they are murdered by the Jiralhanae.
 * The Prophet of Truth transfers command of the Covenant military to the Jiralhanae, while Tartarus declares war on the Sangheili, and the Fall of High Charity begins. Fighting between Sangheili and Jiralhanae forces breaks out all over High Charity. As word spreads, fighting takes place throughout the fleet, as Sangheili and Jiralhanae controlled ships attack one another.
 * The Flood invade High Charity during the battle, entering the city's dome via precision slipspace jump aboard and its embarked Pelicans. The High Prophet of Mercy is attacked by a Pod infector and abandoned by the Prophet of Truth, who now reigns as the Covenant's sole leader.
 * Tartarus attempts to activate Installation 05 by forcing Commander Miranda Keyes to insert the Index into the Control Room's Core.
 * Thel 'Vadamee, with the aid of Sergeant Johnson and Rtas 'Vadumee, kills Tartarus.
 * Commander Keyes aborts the activation of Installation 05, placing the entire Halo Array on standby status. 343 Guilty Spark reveals the existence of the Ark.
 * The Flood takes control of High Charity and many of its warships. Jiralhanae and Sangheili fleets remaining around the city-station continue to destroy each other.
 * The Prophet of Truth departs High Charity for Earth aboard the Forerunner Dreadnought, to join the Battle of Earth. The Jiralhanae forces there are already engaged in fighting with the UNSC. Unbeknown to the Prophet of Truth, John-117 is on the ship, with the intention of "finishing the fight".
 * The prowler Dusk witnesses the battle between Sangheili and Jiralhanae held ships above Delta Halo, both fighting each other pausing only to escalate an immediate outbreak of the Flood from the ringworld. Dusk subsequently flees the battle and links up with Patterson's battle group at Earth.
 * Sangheili Major Voro 'Mantakree kills his shipmaster, Tano 'Inanraree, while he is attempting to allow the Flood to enter the ship. He then assumes command of the ship, the Incorruptible, and becomes the de facto leader of the Second Fleet of Homogeneous Clarity. He leads his new forces to Joyous Exultation, pursued by the Jiralhanae Gargantum and his ships.
 * Imperial Admiral Xytan 'Jar Wattinree plans to lure the Jiralhanae leadership to the Sangheili base world Joyous Exultation and plans an ambush for them. He deploys the newly-promoted Fleet Master Voro Nar 'Mantakree to Onyx to recover the Forerunner technologies there and prevent the UNSC forces there from claiming it themselves. A NOVA bomb captured by the supercarrier Sublime Transcendence devastates the planet moments after 'Mantakree's forces leave, the survivors joining 'Mantakree at Onyx.

November 8:
 * The Forerunner Dreadnought arrives in the Sol system, and proceeds on course towards Earth at near-relativistic speeds.

November 17:
 * The Forerunner Dreadnought enters Earth's atmosphere. John-117 ejects from the ship upon reentry, landing in the jungles near Mount Kilimanjaro.
 * Battle of Voi. The Prophet of Truth uses the Forerunner Dreadnought to activate the Portal, and his loyalist fleet follows it through the portal. The Flood-infested Voi, only to be contained by the Sangheili fleet.

December 11
 * News spreads wide through Sangheili fleets, who take in some instances up arms against their Prophet escorts and, more widely, against the Jiralhanae.
 * Truth and his loyalists arrive at the Ark, pursued by the Sangheili Fleet of Retribution. A massive battle begins over the Ark. All of Truth's vessels are eventually destroyed over the Ark by the Sangheili fleet.
 * Sangheili and human forces fight their way to the Citadel. The Prophet of Truth, the last Hierarch of the Covenant, is executed by Thel 'Vadam with help from the Flood. John-117 stops the Ark from firing the Halo rings.
 * High Charity is destroyed by John-117 after he overloads the city's main reactors causing them to detonate.
 * Rtas 'Vadum evacuates all humans and Sangheili, via the Shadow of Intent, back to Earth.
 * Arbiter Thel 'Vadam, John-117 and Sergeant Johnson battle to the control room of Installation 08. Guilty Spark runs rampant, killing Johnson before being subsequently destroyed by John-117. Installation 08's sentinels turn on the Spartan, Thel 'Vadam, and the Sangheili. The unfinished Installation 04 is activated, devastating the Ark and destroying the entire local Flood infestation including the Gravemind. These final events ended the Human-Covenant War.
 * John-117, Cortana, and Thel 'Vadam escape the Ark. With their escape vessel, cut in half upon slipspace transition, only Thel 'Vadam gets back to Earth.

Trivia

 * A "schism" is a division within a religious sect or denomination. The term "Great Schism" is sometimes used to describe real-world internal religious debates, most notably the East-West Schism, which led to the establishment of the Eastern Orthodox Church, and the Western Schism, which caused a split within the Roman Catholic Church.
 * In Halo: Contact Harvest, the Prophet of Truth foreshadows the Great Schism, noting that if the Sangheili ever separated from the Covenant, the entire government would collapse.
 * According to the Bestiarum, the Unggoy were too indecisive to continue the rebellion and the true political motivation of the Mgalekgolo, if any, remained a mystery.
 * In Halo 3: ODST, it is implied that the Office of Naval Intelligence was aware of internal conflict within the Covenant from early on. During the level Tayari Plaza which takes place on October 20, Buck asks Dare about the Sangheili bodies lying around the city, as they appear to have been killed by the Jiralhanae; Dare responds that said information is classified.

List of appearances

 * Halo 2
 * Halo: Ghosts of Onyx
 * Halo: Uprising
 * Halo 3
 * Halo 3: ODST
 * Halo Legends
 * Origins
 * Halo: Evolutions - Essential Tales of the Halo Universe
 * The Return
 * Halo: Glasslands
 * Halo: The Thursday War
 * Halo: Escalation
 * Halo: Mortal Dictata
 * Halo: Broken Circle
 * Halo 2: Anniversary
 * Terminals
 * Halo: New Blood
 * Halo: Hunters in the Dark
 * Halo 5: Guardians
 * Halo Mythos
 * Halo: Fractures
 * Breaking Strain
 * Halo: Tales from Slipspace
 * Hunting Party
 * Halo: Envoy
 * Halo: Retribution
 * Halo: Legacy of Onyx