Human-Covenant war

Human-Covenant war
Date	February 3rd, 2525 - December 11th, 2552 March 3rd, 2553 (official ceremony)
Location	Orion Arm of the Milky Way galaxy (except for the Battle of Installation 00, which took place outside of the Milky Way).
Outcome	UNSC/Covenant Separatists victory The Covenant collapses Both the Ark and Installation 08 are believed to be destroyed or heavily damaged Flood threat is believed to be neutralized Over half of the Human population exterminated. Some planets abandoned, rendered lifeless and/or uninhabitable Several UNSC planets go dark
Belligerents
Unified Earth Government UNSC CMA Insurrectionists United Rebel Front Covenant Separatists (Post-Great Schism Nov 3, 2552) Fleet of Retribution Forerunner constructs Banished (Late war)
Covenant Empire
Forerunner constructs (Occasionally allied with the UNSC)
Flood
Forces
UNSC Defense Force Covenant Separatists Armed Forces (post-Great Schism)
Covenant Armed Forces
Sentinels, Constructors, Enforcers, Gatherers, Protector Sentinels, and Monitors
Various Flood forms
Casualties
Approximately 23 billion civilian and military casualties. At least 76 planets glassed Reach is glassed and pronouce lost Unknown Separatist force killed, likely in the thousands to hundreds of thousands due to late entry into the war. Unknown amount of Sentinels however likely in the hundreds to thousands from destruction and glassing of Halo Installations.
Heavy casualties for all races Destruction of Covenant Holy City High Charity and Unyielding Hierophant Devastation of Joyous Exultation Most of the Loyalist forces 1 Arbiter At least two Chieftain of the Jiralhanae Prophet of Regret Prophet of Mercy Prophet of Truth
Minor sentinel casualities Destruction of Installation 04 and Installation 08 Installation 00 is heavily damaged Many Sentinels are destroyed 343 Guilty Spark is destroyed
Vast majority of Flood forms are destroyed The Gravemind is killed

The Human-Covenant war, also known as The Great War, was a major interstellar conflict pitting humanity and its United Nations Space Command against the Covenant Empire during the mid-26th century between February 11, 2525 and December 11, 2552. There were two known additional factions of the conflict: the Flood and a small number of surviving Forerunner constructs. Both additional factions proved to be invaluable to the efforts of humanity, as the information taken from Forerunner constructs and the Flood invasion of High Charity were helpful in splitting the Covenant apart in October of 2552.

The war was instigated by the Covenant, whose Prophets discovered that humans were directly related to the Forerunners. In order to keep the Covenant Empire intact, war was declared against humanity. Over the next few decades, the Covenant, with superior numbers and technology, overpowered humanity on many worlds, including heavily defended strongholds such as Reach. Aside from several notable triumphs, the UNSC would only win scattered and costly victories, most of which the Spartan super-soldiers contributed to immensely.

The conflict was closely connected with, and the cause of, the Covenant Civil War, both of which resulted in the final defeat of the Covenant Loyalists and Flood. The final battle took place on December 11, 2552. The official end of war ceremony occurred on March 3, 2553. The war was incredibly costly to both sides, with over twenty-three billion human casualties and enormous Covenant military losses, including the mobile homeworld of High Charity. The war ultimately lasted for a total of twenty-eight years.

Background

Humanity and the Covenant first came into direct contact on February 3, 2525, when a Kig-Yar Frigate, the Minor Transgression, discovered a human ship that had dropped out of slipspace due to a problem with the Shaw-Fujikawa Translight Engine. The Kig-Yar raided that ship and another one. The Harvest shipping operations AI, Sif, found out about the raids as a result of the distress beacon from the ships (although she and an undercover ONI spook on Harvest thought that Insurrectionists, not aliens, were behind the raids). The spook set a trap for the Kig-Yar which resulted in a minor skirmish between Staff Sergeants Nolan Byrne and Avery Johnson and the Kig-Yar privateers. When the Covenant returned with another ship and a contingent of Jiralhanae, the UNSC proposed a meeting (via pictogram) to trade. The Covenant met the UNSC on Harvest, but were only interested in claiming the relics that the Luminary had detected on Harvest, completely oblivious that the humans were the "relics" in question. The meeting was botched after Osmo, a member of the Colonial Militia, was attacked by a nervous Unggoy, part of a second Covenant force sent to look for the relics. As a result, a firefight erupted between the two groups and the Covenant retreated back to their ship.

The Prophets declared Humanity to be an affront to their gods (later propaganda would declare humans had inhabited and "defiled" Forerunner artifacts and worlds), and called for a crusade against the Human species. The Covenant's final objective was nothing less than total genocide.

Unknown to all but the highest echelons of leadership, the campaign to exterminate Humanity was an attempt by the Prophets to maintain political and religious power. In truth, the Prophets had discovered Forerunner objects that the Luminary revealed on Harvest were actually Humans (which the Prophets interpreted as meaning that the Humans were descendants of the Forerunners, or possibly surviving Forerunners). Initially, the Covenant interpreted the glyph from the luminary as "Reclamation." The Forerunner AI 032 Mendicant Bias revealed that the interpretation was incorrect: the glyph meant "Reclaimer." The Prophets Regret and Truth realized that if the Humans were Forerunners, then it was possible to be left behind when the prophesied Great Journey occurred. This stood in direct contradiction to the Covenant religion. The Hierarchs, recognizing that this truth would destroy the Covenant, declared war on Humanity, hoping the truth would perish with their newly declared foe.

The War

Early Battles

Staff Sergeant Johnson leading Colonial Militia during the Covenant invasion of Harvest.

The first battle of the war was the extended, albeit one-sided, ground battle which took place on Harvest. The UNSC managed to delay the Covenant long enough to evacuate many of Harvest's civilians. Eventually, the Covenant used their capital ships to glass the planet's surface.

Cole's fleet destroys the Covenant ship in the Second Battle of Harvest.

The Covenant continued to attack and destroy Humans wherever they were found, using their Luminaries to find Human worlds. Though the UNSC forces fought bravely, inferior technology made any victory difficult - dependent on strategic and numerical superiority, often with the aid of Spartans. Human armor, missiles, magnetic accelerator cannons, and crude slipspace technology were asymmetrically matched with Covenant energy shields, plasma torpedoes, energy projectors, and pinpoint slipspace jumps. The Covenant, fighting a war of extermination, did not need to commit to full ground invasions except in special circumstances. Covenant ships needed only to destroy human space-borne defenses, then reduce the planet's surface to glass with orbital plasma bombardments. Covenant troops were used to soften up UNSC ground forces, or hunt for holy relics. Over twenty-seven years, the Covenant whittled UNSC forces away through firepower and attrition.

Realizing the threat posed to humanity by the Covenant, the UNSC gave Vice Admiral Preston Cole the command of the then-largest fleet in human history with orders to retake Harvest. Cole retook Harvest in 2526, and then spent five years chasing the Covenant around the Outer Colonies, scoring victories at Alpha Aurigae, XI Boötis A, and Groombridge-1830. Meanwhile, the Covenant returned to Harvest, determined to recapture the planet. This led to a five-year long series of engagements on Harvest between the Covenant and the UNSC.

The Apex and the Arbiter (2531)

The Prophet of Regret converses with the 17th Arbiter on the destruction of the human race.

Despite their major numerical and technological advantages over humanity, by 2531, the Covenant High Prophets had realized that the task of destroying an entire sapient species had a logistical burden beyond anything that the Covenant military could muster without leaving Covenant space defenseless. Despite the UNSC's disadvantages, the Prophets considered the UNSC's armed forces powerful enough to pose a threat to the Covenant. These concerns would be justified by extreme Covenant losses during the war's culmination in 2552. The Prophet of Regret dispatched an Arbiter to Harvest to claim a Forerunner artifact buried under the north pole of Harvest. Acquisition of advanced technology would allow a quick, decisive victory in the conflict.

Preston Cole counter-attacked by sending a force composed of UNSC Spirit of Fire and UNSC Prophecy back to Harvest after receiving a message from an ONI Prowler. The battle resulted in victory for Cole, despite major casualties. Upon discovering that the Covenant, under the command of 'Moramee, had excavated Forerunner artifacts in the northern polar region, Captain James Cutter deployed ground forces to remove the Covenant occupation. After a heated fight on the planet's surface, the UNSC forces were able to examine the artifact, a star map, and realized in horror that information had led the Covenant to another UEG colony: Arcadia.

UNSC Spirit of Fire engages a Covenant CPV-class heavy destroyer in Shield 0459.

As predicted, the Covenant followed the information from the artifact to Arcadia. The Covenant hoped that the planet would contain more Forerunner artifacts for them to claim, and while they only found a complex of ruins, information garnered from them led them to Shield 0459. Spirit of Fire followed and removed the Covenant presence from the planet. However, 'Moramee's capture of an important civilian researcher forced Captain Cutter to pursue the Covenant without reinforcements.

On the Shield World, the crew of Spirit of Fire eventually discovered that the Covenant needed Professor Anders, by definition a Reclaimer, to activate the Apex and claim the huge fleet of Forerunner starships within. A group of Marines, together with Spartan-II Red Team, rescued the researcher and destroyed the Shield World. The Arbiter was also killed by John Forge during the battle, though the Prophet of Regret escaped.

Spartan-III (2531)

Main article: SPARTAN-III Program

Despite the well-publicized victory at Harvest, the UNSC was already on the way to losing the war. A number of colonies had already been glassed by the Covenant or abandoned, including Eridanus II, Dwarka, and Chi Ceti IV. The UNSC's best hope for conventional victory lay with the SPARTAN-II Program, a program designed to create super-soldiers, originally to combat Insurrectionists. Despite their incredible combat ability, there were never enough Spartans to meet demand for wide scale deployment. Recognizing this, the Office of Naval Intelligence authorized the creation of the SPARTAN-III Program. The brainchild of Colonel James Ackerson, these Spartans would be trained with a greater emphasis on stealth and teamwork, and would be sent on missions against high-priority targets with suicidal odds.

Crisis (2534-2535)

A member of Gray Team at the Battle of the Rubble.

With the majority of the Outer Colonies glassed or abandoned, the UNSC faced an economic crisis. Some of their most important Agricultural Worlds had been destroyed, leading to widespread food shortages. On Charybdis IX, riots broke out. Meanwhile, Covenant forces began to encroach on the Inner colonies. In response, the UNSC issued United Nations Space Command Emergency Priority Order 098831A-1, "The Cole Protocol." No UNSC vessel could be permitted to lead the Covenant to Earth, or any other human population center. Furthermore, all movement through space was restricted to UNSC Navy vessels. Insurrectionist attacks increased in the face of what they perceived as a removal of their right to freedom of movement. This was to culminate in the discovery of Insurrectionists using Covenant weapons modified for human use from seemingly renegade Kig-Yar. Shocked, the UNSC saw this as a major threat to security. The Covenant viewed it as heresy that humans would modify their weapons, and as a result the Prophet of Regret dispatched Thel 'Vadamee to destroy the source of the modified weapons: The Rubble.

Fleeing from the Battle of Charybdis IX, UNSC Midsummer Night chased an Insurrectionist freighter to the Rubble and discovered that the Insurrectionists there had actually formed an alliance with a colony of Kig-Yar. These Kig-Yar supplied the weapons, and the Insurrectionists modified them. The crew of Midsummer Night, including its captain, Lieutenant Jacob Keyes, were captured, but later escaped and aided Spartan-II Gray Team and the Rubble's citizens stop an assault from the Kig-Yar leader, Reth, and 'Vadamee's forces. It later transpired that the Prophet of Truth had ordered the Kig-Yar to ally with the humans so that they could discover the location of Earth from stolen navigation data or through tracking devices in the weapons. Through this, the Covenant found two more worlds to attack.

By the time of the Battle of Jericho VII in 2535, most of the Outer Colonies had been destroyed.

Continuing war (2536-2551)

Humanity, heavily out-gunned, lost much ground to the Covenant.

Main article: Siege of the Inner Colonies

On June 1, 2536, the Covenant finally broke into the Inner colonies. From this point on, the war ground on in a predictable pattern; costly victories on the ground for UNSC forces, and near total Covenant space superiority. The UNSC managed to deal a heavy blow to the Covenant in 2537 with the destruction of the Covenant manufacturing plant K7-49 in Operation: PROMETHEUS, and again during the Siege of the Atlas Moons in the same year. However, these victories were offset by the loss of New Constantinople, its colonies at Leonis Minoris, and the total destruction of the force of Spartan-IIIs deployed to destroy the Covenant base.

Throughout the 2540s, the UNSC was dealt ever greater blows with the death of the Spartan-II Sheila during the Battle of Miridem in 2544, defeat during the Fall of Arcadia and the loss of Paris IV in 2549. A major human success was Operation: TORPEDO in 2545, the loss of 298 Spartan-IIIs were considered acceptable losses by UNSC High Command. The Spartan-II Raid on the Third Fleet of Glorious Consequence also proved the Covenant Empire was overwhelmingly powerful, but not invincible.

Of the few wins in the 2540s for the UNSC was the Battle of Psi Serpentis in 2543. This battle became colloquially known as Admiral Cole's last stand due to the presumed death of Admiral Preston J. Cole. In addition to the alleged death of Cole, over 300 Covenant vessels, two fleets worth, were completely vaporized when UNSC nuclear missiles detonated inside the atmosphere of Viperidae, a super massive gas giant. This detonation spurred spontaneous fusion at the core of Viperidae, temporarily turning the super gas giant into a brown dwarf star. Cole's achievements in this battle alone were only rivaled by the destruction of Unyielding Hierophant and the actions of John-117 throughout the course of the war. A painting depicting the battle, titled "Admiral Cole's Last Stand" was created and by 2552, it hung on the wall of the HIGHCOM Facility Bravo-6 in Sydney, Earth. The battle was one of the most significant and strategically important victories for the UNSC in the entire war.

Towards the end of the war in 2552, the Office of Naval Intelligence was resigned to the fact that humanity may only have months left before the Covenant destroyed the remaining Inner colonies and moved on against Earth. To buy time, and perhaps survival, HIGHCOM ordered all available Spartan-IIs to return to Reach and leave on Operation: RED FLAG, a mission to locate the Covenant homeworld, capture a Prophet and force the Covenant into a cease-fire.

The Final Year (2552)

The last year of the war saw humanity's largest defeat, but also saw several of their greatest victories, coupled with the destruction of the Covenant as a galactic power. On Sigma Octanus IV, the Covenant were defeated. On the ground, the Spartan-IIs secured a Forerunner artifact covered in symbols that the Covenant tried to transport out of Côte d'Azur. However, in space, the Covenant placed a Spy probe on UNSC Iroquois, which led the Covenant to the UNSC's stronghold and main headquarters, Reach.

The Fall of Reach that followed resulted in staggering losses for both sides, but ended in a Pyrrhic Covenant victory. UNSC Pillar of Autumn was among the surviving UNSC ships which fled the battle, and made a unique jump, as described by AI Cortana as using symbols on the retrieved artifact from Sigma Octanus IV, were in fact very old star charts. The coordinates led to the Forerunner ring world of Halo.

The tide turns (2552-2553)

Pillar of Autumn pushes through the Covenant blockade and escapes Reach.

The Covenant suffered a major military defeat at Installation 04. Here, the Human survivors from the Halcyon-class light cruiser Pillar of Autumn formed an effective resistance to the Covenant forces in-system. Unwilling to risk damaging the sacred ring, the Covenant was forced to fight the Humans on Halo's surface rather than using its usual glassing tactics. The Covenant found the Humans very adept at fighting on the surface, employing their firearms and vehicles in classic guerrilla raids. Unable to counter the tactics employed by the Humans, the Covenant was defeated again and again, including one instance when humans boarded their grounded cruiser, the Truth and Reconciliation, and successfully escaped with a group of captives, including the captain of the Pillar of Autumn, Captain Jacob Keyes. The battle on Halo then suddenly took a turn for the worst for both sides when the Covenant accidentally released an ancient and deadly parasitic race called the Flood. The Flood, having been imprisoned within Halo for many thousands of years, spread quickly throughout the ring, killing or assimilating every unsuspecting human and Covenant in their path.

During the course of the battle, the Spartan-II known as John-117 discovered the true nature of Halo and proceeded to detonate the crashed Pillar of Autumn's engines, destroying the ring, and escaped, much to the Covenant's dismay. Not only had the Covenant war machine been denied victory, a sacred artifact of the gods themselves had been destroyed. The result of the battle devastated Covenant morale in the short term. The destruction of Halo and the later loss of the flagship Ascendant Justice to the surviving UNSC forces led to Supreme Commander Thel 'Vadamee being disgraced and demoted before being branded with the Mark of Shame, leaving him dead in the eyes of the Sangheili. Only the intervention of the Prophet of Truth prevented 'Vadamee's certain execution. He was instead given the rank of Arbiter and sent to quell a Heretic uprising that had taken root on the Gas Mine around Threshold.

The UNSC Home Fleet prepares to engage the Covenant Navy.

Shortly after the defeat at Halo, the Covenant had amassed a large fleet consisting of five hundred Jiralhanae-led warships, apparently intended to assault Earth directly. The Covenant discovery of Earth was an accident after the Pious Flea had been intercepted by the UNSC stealth ship Apocalypso. After retrieving a Forerunner artifact, Apocalypso made a Slipspace jump directly to Earth. When the ship tumbled into real space and crashed on the moon, the Pious Flea sent a message to the heart of the Covenant military, containing reconnaissance data, photos, star maps, and the coordinates of the Forerunner Artifact, which was now on Earth. However, the Covenant had not identified Earth as the Human homeworld, and the Unyielding Hierophant's fleet was never expressly identified as an invasion force; this is merely a reasonable assumption made by the Human forces upon discovery of the fleet's destination of Sol.

This leaves the exact nature of the fleet's mission uncertain, as there is no definitive proof that the Covenant were intending to attack their enemy's homeworld. Nonetheless, the human survivors of Installation 04 correctly assessed the fleet to be a direct threat to Earth, and, using a captured Covenant flagship, lured the armada into a trap and destroyed it.

A few weeks after this defeat, the Prophet of Regret led a small fleet of fifteen ships to Earth in order to locate a Forerunner artifact known as the "Ark." Though hopelessly outgunned by the UNSC's new orbital defense grid of MAC guns, the Prophet of Regret's flagship managed to break through the Human defenses to New Mombasa. The Covenant ground troops quickly spread through the city, destroying both military and civilian resistance. When a counter-attack by the Marines and John-117 inflicted heavy losses Regret was forced to flee, leaving his fleet to burn. His carrier jumped into Slipspace from within the city, damaging it severely.

Unfortunately for Regret, four Human ships, In Amber Clad among them, had followed them through their own Slipspace rupture to Installation 05. With the orders "Find out why he came to Earth; why he came here," John-117 was hard-dropped with a complement of Orbital Drop Shock Troopers to Delta Halo's surface. Led by John, the Humans forced their way through Regret's forces until they had reached the Prophet himself. At that moment, High Charity, having learned of Delta Halo, arrived and launched multiple waves of Phantom dropships to aid Regret. However, they were withdrawn by the Prophet of Truth as part of his plan to remove the Sangheili from power in the Covenant. However, Truth had perhaps underestimated the full impact his 'reforms' would have on the Covenant's military campaign. John-117 ultimately assassinated Regret, dealing a heavy blow to the Empire's political structure. The Prophet of Truth then gave the order to glass the temple in which Regret was residing. John-117 barely escaped, only to be captured by the Gravemind.

The Great Schism begins.

Meanwhile, the majority of the Human forces on In Amber Clad had traveled to Delta Halo's Library to obtain the Index, the key to a successful firing of the Halo array. Originally, the Covenant had been unaware of the Index's importance. Fortunately, Arbiter Thel 'Vadamee had obtained 343 Guilty Spark, the monitor of Installation 04, while destroying the Heretic base. The monitor, known to the Covenant as an Oracle, told the Prophets of the Index and the Arbiter was sent to retrieve the "Sacred Icon." The mission was complicated though by the unexpected release of the Flood. Despite this, the Arbiter successfully reached the Library and prevented the Humans from claiming the Index, kidnapping Miranda Keyes and Sgt. Johnson. However, the Index was stolen from the Arbiter by the Jiralhanae Chieftain Tartarus, who was under the Prophets' orders to retrieve the Index, and kill the Arbiter. Although unsuccessful at the latter goal, with the Index secure, the Prophets then ordered the Jiralhanae to begin eradicating the Sangheili, thus beginning the Covenant Civil War. Ultimately this led to the death of Tartarus at the hands of Vadamee and Johnson. A temporary alliance was formed between the Separatists and the Human forces. Delta Halo was prevented from firing by Miranda Keyes and in the chaos of High Charity, the Flood infested the Prophet of Mercy, leaving the Prophet of Truth firmly in control over the Covenant.

The Battle of Onyx

Spartans at the Battle of Onyx.

Long before the events surrounding Halo, the classified UEG colony of Onyx had been designated the headquarters and training ground for the SPARTAN-III Program. However, the UNSC had no idea that the planet was in fact a huge Forerunner construct, integral to the Halo Array, and containing trillions of Sentinels. After John-117's destruction of Alpha Halo, the Sentinels were roused by the disruption of the Halo network and the portal leading into the Shield World at the planet's core began to close. At this time, a small group of Spartan-IIIs were training in a top honors exercise on the surface. After the humans failed to exchange the proper counter-responses, the Sentinels relabeled the "Reclaimers" as aboriginal subspecies and began to exterminate them. Led by Kurt-051, the Spartan-IIIs fought a guerrilla war against the Sentinels until Doctor Catherine Halsey arrived on Onyx and explained the wider situation. Knowing that the Forerunner technology buried in Onyx's core could turn the tide of the war for humanity, Halsey used Forerunner technology to send a message to Fleet Admiral Sir Terrence Hood, requesting reinforcements. Hood deployed Blue Team to Onyx, who stole a Covenant destroyer to reach the planet in time.

Meanwhile, the Covenant Separatists under the leadership of Imperial Admiral Xytan 'Jar Wattinree had deployed a fleet to Onyx to claim the "sacred relics" for their fight against the Jiralhanae and the other Loyalists. Xytan would not live to hear of the results of this mission, as he and the majority of his fleet were annihilated by a UNSC Nova bomb recovered from Reach. After Blue Team made landfall, Fleet Master Voro Nar 'Mantakree's fleet arrived at Onyx, destroying hundreds of orbiting Sentinels before engaging UNSC forces in the Forerunner city below. 'Mantakree personally led the Covenant forces on the surface, before the UNSC Battlegroup Stalingrad arrived and used indirect help from the Sentinels to destroy the majority of the Separatist fleet before being wiped out by reinforcements from Joyous Exultation, with only one ship escaping.

On the surface, the Spartans had discovered the Core Room Antechamber and were preparing to enter the Shield World. They managed to hold off hundreds of Covenant troops before being forced to retreat into the Core, while Kurt-051 sacrificed himself by detonating a couple of FENRIS Nuclear Warheads, killing the entire Separatist force. Following the Core being sealed, Onyx broke up into trillions of Sentinels, guarding the construct. With the Covenant Separatists dangerously depleted, the warlike Sangheili were finally forced to ally with their hated enemy, humanity.

Arrival of the Flood and Sangheili/Human Victory (2553)

The Sangheili and Humans make ready to finish Truth and the Covenant at Installation 00.

The battle between Covenant Separatists & Loyalists, raging over Installation 00.

“In memory of those fallen in the defense of Earth and her Colonies. March 3, 2553.”

— Hillside Memorial

Following the Flood infestation of High Charity, the High Prophet of Truth led the remaining loyalist Fleet to Earth to complete what the previous mission to Earth had not. Little did he know that a Spartan-II had stowed away with him on board his Dreadnought. By the time Truth arrived at Earth, a full-scale battle in space and on the ground was underway between UNSC and Covenant Fleets.

After a slug-fest lasting several weeks, the UNSC Homefleet was nearly wiped out. However, the Covenant Loyalist fleet was also vastly reduced and focused on securing an enormous unearthed Forerunner structure near the ruins of New Mombasa. With the arrival of John-117, the remaining UNSC forces launched an assault on the area, sweeping aside all Covenant resistance and finally launching an all-out attack on the Prophet of Truth's Forerunner ship.

Unfortunately, even in-atmosphere MAC strikes proved ineffective against the Forerunner dreadnought, and Truth quickly activated Voi's portal and escaped. Events were further complicated by an unexpected attack by the Flood. Thanks to the timely arrival of the Sangheili, the Flood force was vanquished but not before Master Chief recovered a recording from Cortana, who had stayed behind on High Charity. Cortana's message told of a means to stop the Flood on the other end of the portal. A small fleet of Human and Sangheili forces was sent through the portal, leading them to the Ark, just outside the Milky Way galaxy. The Covenant Fleet above the Ark immediately attacked. Though the joint Human-Sangheili fleet was outnumbered 3-1, the battle ended in defeat for the Covenant Loyalist Fleet. Simultaneous to the space battle between Jiralhanae and Sangheili ships, UNSC forces were deployed to the surface of the Ark.

The final battle of the war was fought in December 2552 as Truth attempted to activate the Halo rings. Led by John-117, the Human forces, despite fanatic resistance managed to smash through the remaining Covenant forces on the ground. The battle was complicated by the arrival of High Charity. As the Flood began to spread, John and the Arbiter went on to thwart Truth, who died in mid-Flood-infection at the Arbiter's hand. John-117 deactivated the Halo Array and brought an end to that threat as well. With the Covenant forces completely shattered, Truth's death marked the effective end to the war. The Flood still remained a threat, but were destroyed by John-117, the Arbiter, Cortana and Sergeant Johnson by firing the Halo over the Ark, destroying the parasite and the installation. Although Forward Unto Dawn managed an emergency slipspace jump, the portal collapsed splitting the vessel in half. Trapped in the rear section of the frigate, John-117 placed himself into cryosleep until he could be retrieved, eventually drifting to a Forerunner world. The UNSC's greatest soldier, and humanity's champion, was presumed dead.

The ceremony held to honor the fallen.

Some months later, in March 3 of 2553, a monument was erected on a hillside near the Portal to the Ark to commemorate the billions of men and women killed during the war, and John-117's name was included as he was presumed MIA by the UNSC, as no Spartan could be declared dead for such morale purposes. Lord Hood shook hands with the Arbiter to signify an end to hostilities. The Covenant Civil War would continue for at least another six years between Sangheili and Jiralhanae factions, further depleting their now crumbling infrastructure. The fate of the Prophet's was especially ironic, as the infestation of High Charity resulted in the near extinction of their race. The most destructive conflict in human history had ended in victory, but at a staggering cost. Both the UNSC and the Covenant Separatists then turned to the enormous task of rebuilding their once great societies after that.

Factions

Leaders	Homeworld	Military Forces
United Nations Space Command
UNSC Security Council	Earth	Unknown, likely in the hundreds of millions or billions.
Covenant
Hierarchs, High Council	Multiple worlds - different member races, High Charity (Political and Religious capital)	Exact numbers are unknown, but most likely larger than Humanity's forces.
Covenant Loyalists
Prophet of Truth	Doisac, Eayn, and Palamok.	Exact numbers are unknown, but are assumed equal to or larger than the Covenant Separatists' forces.
Covenant Separatists
Arbiter Thel 'Vadam, Imperial Admiral Xytan 'Jar Wattinree, Fleet Master Rtas 'Vadum	Sanghelios, Balaho, and Te	Exact numbers are unknown, but are assumed equal to or smaller than the Covenant Loyalists' forces.
Flood
Gravemind	Unknown, extra-galactic.	Massive; probably in the trillions.
Forerunner Constructs
Unknown, Forerunner Artificial intelligence constructs including Monitors such as 343 Guilty Spark.	Created on most constructs.	Sentinel count believed to be in the tens of trillions or possibly quadrillions, as there are multiple Shield Worlds and Onyx alone was composed of trillions of Sentinels.

Timeline

2524 (Pre-War)

• A damaged human civilian freighter, Horn of Plenty, suffers a Slipspace drive malfunction from Harvest to Madrigal, forcing the unmanned freighter to exit back into normal space. A Covenant vessel, Minor Transgression, comes into contact after hours of the freighter's isolation. The Covenant vessel targets the freighter, and a Kig-Yar boarding crew enter.

2525

• The first battle between Humanity and the Covenant takes place prior to the outbreak of the war. Humanity attempts to gain a truce between the races through a pictogram of trade and peace between the Covenant and Humanity, but to no avail. (Pre-War)
• The Covenant launch a full-scale assault on Harvest, glassing the planet. Afterward, the Minister of Fortitude, Vice-Minister of Tranquility, and the Philologist become the High Prophets of Truth, Regret, and Mercy, and declare war on Humanity.
• The Human-Covenant war begins
• Shortly after the attack on Harvest, the colonies of Green Hills and Second Base are glassed.
• The Battle of Chi Ceti takes place.
• The Battle of Biko takes place.

2526

• Battle of Bliss. Human colony Bliss is glassed by a fleet of 45 covenant ships as the defending fleet of 3 ships was destroyed with little to no cost to the Covenant Fleet.
• Second Battle of Harvest. The UNSC and Covenant meet in ship-to-ship combat for the first time; the Covenant are outnumbered and out gunned, nevertheless the battle is a high priced victory for the UNSCDF, costing the UNSC 13 ships or about one third of the fleet which was assembled to encounter the threat. The Covenant would return to Harvest later in the year, and the battle for the planet, dubbed by the UNSC as the Harvest Campaign, would last for the next five years.
• Battle of Alpha Aurigae. Another ship-to-ship battle, where the UNSC outnumber the Covenant almost 10-1, but lost a third of their ships. This was one of the rare naval "victories" for the UNSC
• Battle of Circinius IV. Covenant forces launch a massive surprise attack on one of the UNSC's most prestigious military academies, the Corbulo Academy of Military Science. This was a major blow to the UNSC as many of their brightest future officers were annihilated in the attack, with only three cadets surviving.

2528

• Battle of XI Boötis A, the UNSC fleet of 70 warships destroy 8 enemy vessels, losing 30 of their own in the process
• Madrigal is glassed by The Covenant

2530

• The Covenant destroys the UEG colony world of Eridanus II
• Battle of Groombridge-1830, 11 UNSC Destroyers are lost in attempt to defeat a Covenant Fleet of 3 warships

2531

• The UNSC finally manages to retake Harvest, ending the five-year long Harvest Campaign in a UNSC victory.
• The Battle of Arcadia takes place.
• The Battle of Shield 0459 takes place.
• Kurt-051 is kidnapped by Section III of ONI to train the classified Spartan-IIIs, in a need for more supersoldiers to fight the Covenant.

2532

• The Battle of Vodin takes place.

2535

• The Covenant destroys the UEG colony world of Jericho VII in the Battle of Jericho VII.
• The Battle of Charybdis IX takes place.
• The Battle of the Rubble takes place.
• In the course of four short years, UNSC forces have been hammered, despite excellent leadership and tactical brilliance. It is simply a matter of being outgunned; Covenant kill ratios tend to top three to one in ship-to-ship combat. By 2535, virtually all of the Outer Colonies have been glassed by the Covenant.

2536

• Covenant forces begin to swarm into the Inner colonies. For several years the war falls into a pattern: humans win isolated battles, typically during ground operations, but at a horrible cost. In space combat, the humans are losing at a precipitous rate, and one by one, the colonies fall.

2537

• Discovery of Covenant Manufacturing Plant K7-49 at the Battle of New Harmony.
• Battle of New Constantinople, Covenant glassing of New Constantinople.
• Battle of Leonis Minoris, Covenant destruction of Leonis Minoris.
• Siege of the Atlas Moons was a rare victory for the UNSC, as victories in space-based fighting were uncommon for the UNSC Fleet.
• Operation: PROMETHEUS: UNSC Victory. Spartan-III Alpha Company is wiped out by Covenant forces.

2539

• Battle of Kholo, Covenant forces glass the colony of Kholo.

2543

• On March 6 the Battle of 18 Scorpii takes place. In the battle prior-unknown Independent/Insurrectionist human forces assist three UNSC destroyers in defeating a Covenant CPV-class heavy destroyer.
• Vice Admiral Preston J. Cole is presumed to have made his last stand at the Battle of Psi Serpentis on April 18. Over 300 Covenant ships were destroyed in the battle.

2544

• Battle of Miridem, the Spartan-II Sheila is killed while protecting Dr. Catherine Halsey on Miridem. Halsey is subsequently captured by Covenant forces, and is placed on board a Covenant assault carrier in the Third Fleet of Glorious Consequence.
• Raid on the Third Fleet of Glorious Consequence, following Halsey's capture by the Covenant, the Office of Naval Intelligence initiates an operation to rescue her with the assistance of five Spartan-IIs. The operation is a success, and Halsey is rescued, at the cost of two of the Spartans.

2545

• Operation: TORPEDO: UNSC victory. All participating Spartan IIIs, with the exception of Tom-B292 and Lucy-B091 of Spartan-III Beta Company are killed by Covenant forces.
• Battle of Draco III. Covenant kill all UNSC ground forces and captured thousands of civilians. Later a Spartan squad arrive and kill all Covenant forces only to find that the civilians were killed by ravenous, raging Unggoy and Kig-Yar.
• The Battle of Actium takes place.

2546

• The Battle of Sargasso is fought, leading to a Covenant victory.
• Battle of New Llanelli, Covenant victory.

2547

• The UEG colony of Skopje is destroyed by the Covenant.

2548

• The Battle of Meridian takes place.

2549

• Siege of Paris IV, Covenant victory.
• Fall of Arcadia, Covenant victory, Arcadia is glassed.

2550

• Minab is destroyed.

2551

• Concord is attacked by the Covenant.
• Meridian is finally glassed.

2552

April

• Battle of Fumirole. Thom-A293 is killed and Catherine-B320 loses her arm.

July

• Battle of Sigma Octanus IV. The single greatest UNSC victory since Harvest. However, the Covenant gain what they seek: the location of Installation 04. They also discover the Human presence on Reach.
• The Covenant discover Reach, and send in an advance invasion force, beginning the Fall of Reach.

August

• Battle of Tribute. Along with other colonies in the Epsilon Eridani System, Tribute is invaded by Covenant forces. The colony is not glassed instantly, but remains under siege by Covenant forces for some time.
• Battle of Verge. A Covenant Beacon transmitting helium-3 for ships blockading Tribute is destroyed by Team Black.
• Battle of Line Installation 1-4. A UNSC ship on a covert mission, as well as a Covenant Assault Carrier, crash on a remote moon with a Forerunner relic. In the ensuing engagement, the surviving UNSC forces side with the Covenant against the installation's defense systems.
• The Fall of Reach ends. On August 30, 314 Covenant ships destroy over 130 UNSC ships and 20 ODPs for the loss of at least two-thirds of their fleet. It is a major Covenant victory: Reach is the last major stronghold before Sol. UNSC Pillar of Autumn escapes.

September

Part of the wreckage of the destroyed Installation 04.

• Battle of New Jerusalem. Following an attack on the UEG colony of New Jerusalem, the 26th Marine Expeditionary Force is sent to reinforce the UNSC forces already present. The colony is eventually lost to the Covenant and the survivors fall back to Earth.
• Battle of Installation 04. Pillar of Autumn engages the Covenant, Halo expedition. After four days the battle degenerated into a four-way melee as the Flood organisms are released and Forerunner constructs, Sentinels seek to contain the outbreak. The crew of the Pillar of Autumn are instrumental in preventing the Flood from escaping and the installation from firing by destroying the installation. There are only a handful of survivors.
• Skirmish over Threshold. UNSC survivors from the Battle of Installation 04 rally in orbit over Threshold. Using their limited resources to the fullest they manage to capture the Covenant vessel Ascendant Justice and use it to escape.
• Raid of Reach. John-117 and some of the survivors of the Battle of Installation 04 raid Reach to rescue a Spartan-II team trapped on Reach by a Covenant Fleet. They rescue the Spartan squad leaving a great deal of damage to the Covenant Fleet ships and the ground forces.
• Operation: FIRST STRIKE. Six Spartan-II super soldiers route and destroy a fleet of 500 Covenant warships preparing to jump to Earth. This is the single greatest victory, for the humans during the entire war and the single greatest loss to the Covenant.

October

• Battle of October 10 - Battle Group Rhino detects and engages twelve unidentified ships near Enceladus.
• Battle of Earth. 15 Covenant ships assault Earth, defended by the UNSC Home Fleet and 300 ODPs. The Covenant were not expecting the heavy human presence, as well as their new orbital MAC defenses, and are completely destroyed, save for the Solemn Penance and the Pious Inquisitor. However, a fleet of Covenant capital ships appears soon after, prolonging the battle.

November

• Battle of Installation 05. Regret's Assault Carrier from the initial invasion of Earth retreats to Installation 05, pursued by four small UNSC warships. Only one, UNSC In Amber Clad, arrives in time to participate in the battle.
• The Prophet of Regret is assassinated by John-117.
• The Civil War of the Covenant begins. Covenant forces are thoroughly divided between the Sangheili and the Jiralhanae. Every race in the Covenant takes sides.
• The Prophet of Mercy is later killed by a Flood Infection Form.
• First Battle of High Charity. The Flood eventually takes control of UNSC In Amber Clad, and enters a slipspace to invade the Covenant holy capital, High Charity. 
• Again, the installation is prevented from firing and the Flood appear to take control of the installation and High Charity.
• Battle of Onyx. The destruction of Installation 04 wakes dormant Forerunner installations, including the Sentinels on Onyx which then threaten the UNSC base there. The Spartan-IIs of Blue Team fight their way off of Earth and commandeer a Covenant destroyer, Bloodied Spirit, to relieve Onyx. Covenant and UNSC ships converge on Onyx but ultimately all are destroyed except for UNSC Dusk. UNSC survivors retreat within the Onyx Shield World.
• The Battle of Earth continues. The Covenant Loyalists led by the Prophet of Truth arrive at Earth in force, to reinforce the Covenant forces already present. During the following week, Marines, with help of the Fleet of Retribution division within the Covenant Separatists, pushed back the Loyalist invaders.

December

• Battle of Installation 00. The Prophet of Truth is killed, the Flood is eradicated, and John-117 is left to drift in the rear half of Forward Unto Dawn.
• The Human-Covenant war ends.

2553 (Post-war)

March

• While the fighting finished in December, the official end of war ceremony did not commence until March, with the UNSC and their allies emerging victorious. The victors erect a monument on a hillside near the Ark's Gateway to commemorate those fallen. Despite being listed MIA as per protocol, the UNSC widely believe John-117 to be dead. The Sangheili then depart for the return to Sanghelios.

Unknown

• The Battle of Hat Yai takes place in either 2528 or 2529.
• Asmara and Cote d'Azure are attacked at some point before 2530.

Trivia

• Humanity had encountered some Covenant species before the war: Unggoy, Huragok, Kig-Yar, and Jiralhanae, in that order.
• Avery Johnson was the only human to witness both the beginning and end of the Human-Covenant war. He was present when Harvest was attacked and saw Truth killed, which signified the end of the war.
• Both the year the war started (2525) and the year the war ended (2552) are a reference to the number 7 (2+5=7).

Gallery

Pillar of Autumn escaping Reach

The Great Schism begins

The UNSC Home Fleet just before the Battle of Earth.

Appearances

Halo: Combat Evolved (First appearance) Halo: Combat Evolved Anniversary Halo 2 ​Halo 2: Anniversary Halo 3 Halo 3: ODST Halo Wars Halo: Reach Halo: The Fall of Reach Halo: The Flood Halo: First Strike Halo: Ghosts of Onyx Halo: Contact Harvest Halo: The Cole Protocol Halo: Evolutions - Essential Tales of the Halo Universe Stomping on the Heels of a Fuss Midnight in the Heart of Midlothian Dirt Headhunters Blunt Instruments The Mona Lisa Palace Hotel Human Weakness The Impossible Life and the Possible Death of Preston J. Cole The Return Halo Graphic Novel Halo: Uprising Halo Wars: Genesis Halo: Helljumper Halo: Blood Line Halo Legends Homecoming Odd One Out (Non-canon appearance) Origins Prototype The Babysitter The Package i love bees Halo 4: Forward Unto Dawn Halo 4 (Cutscene and simulation) Halo 5: Guardians (Simulation)