Human-Covenant War

"Oh, death was never an enemy of ours! We laughed, knowing better men would come, and greater wars: When each proud fighter brags He wars on death, for lives: not men, for flags."

- "The Next War"

The Human-Covenant War, also known as The Great War, was a major interstellar conflict pitting the Unified Earth Government and its United Nations Space Command against the Covenant Empire during the mid-26th century between February 11, 2525 and March 3, 2553. There were two 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 the 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 intact, war was declared against humanity. Over the next few decades, the Covenant, with superior firepower, numbers and technology, overpowered humanity on hundreds of worlds, including heavily defended strongholds such as Reach. The Humans would only win scattered and costly victories.

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 official cessation of hostilities occurred on March 3, 2553. The war was incredibly costly to both sides, with over twenty-three billion humans and likely hundreds of millions of Covenant killed during the hostilities and further heavy casualties during the Flood plague.

Declaration of War (2525)
Humanity and the Covenant first came into direct contact in 2524, 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 Kig-Yar privateers. When the Covenant returned with another ship and a contingent of Brutes, 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, but were completely oblivious that the humans were the "relics". The meeting was botched after Osmo, a member of the Colonial Militia, -- was attacked by a nervous Grunt -- who was 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 (supposedly because Humans inhabited and "defiled" areas which were once Forerunner), and called for a crusade against the Human species. This "crusade" would eventually turn into a mass genocide, meaning the deliberate or systematic destruction of a specific group, in this case: all human life.

The campaign to exterminate Humanity was an attempt by the Prophets to keep their power, under the disguise of a holy crusade. The Prophets found out that the Forerunner objects that the Luminary revealed on Harvest were actually Humans (which the Prophets interpreted as meaning that the Humans were descendants of the Forerunner, or possibly surviving Forerunner). Initially, the Covenant interpreted the glyph from the luminary as "Reclamation". Startlingly, the Forerunner AI Mendicant Bias revealed that the interpretation was wrong: the glyph meant "Reclaimer". The Prophets (Regret and Truth) realized that if the Humans were actually Forerunners, then it was possible to be left behind when the Great Journey occurs. This stood in contradiction to the Covenant religion, which held that no one would be left behind in the Great Journey. The Hierarchs, recognizing that this truth would destroy the Covenant, declared war on Humanity, hoping the truth would perish alongside their declared foe.

The first battle of the war was the extended though one-sided ground battle which took place on Harvest, in which 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.

Open War (2525-2552)
From that point on, the Covenant continued to attack and destroy the Humans where ever they were found, using their Luminaries to find Human worlds. Though the UNSC forces fought bravely, their inferior technology and numbers meant that even a close victory was far from guaranteed. The Covenant also had an advantage in that they didn't need to fight planet-side to destroy the enemy; their ships simply needed to destroy the Human's space-borne defenses and any other threats around the planet, and then reduce the planet's surface to glass with orbital plasma bombardments. The few victories achieved by the UNSC were due to special tactical maneuvers, as human missiles and magnetic acceleration weapons were unable to compete with Covenant energy shields and plasma torpedoes. Over twenty-seven years, the Covenant whittled down the UNSC planet by planet.

Realizing the threat posed to humanity by the Covenant, the UNSC Colonial Military Administration 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, fighting them and 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)


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. In spite of the UNSC's inferiority in comparison to the Covenant, the Prophets apparently considered their armed forces to be powerful enough to pose a threat to the Covenant proper. The Prophet of Regret dispatched an Arbiter to Harvest to claim a Forerunner artifact buried under the north pole of Harvest.

Preston Cole counter-attacked by leading a fleet composed of the and the  back to Harvest after receiving a message from an ONI Prowler. The battle was a human victory 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 surface, the UNSC forces were able to examine the artifact, apparently some kind of star map, and realized that information from the map had led the Covenant to another UNSC colony: Arcadia.



As predicted, the Covenant followed the information from the artifact to Arcadia. The Covenant wished that the planet would contain more Forerunner artifacts for them to claim and possibly use to activate the Apex, but found only ruins. The 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 to a Flood-controlled Shield World without reinforcements.

The crew of the Spirit of Fire eventually discovered that the Covenant needed Professor Anders to activate the Apex and claim the huge fleet of Forerunner starships held there. 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)
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 sole hope apparently lay with the SPARTAN-II Program, a secret program to create super soldiers originally to combat Insurrectionists. However, there were not enough Spartans to turn the tide of the war in favor of humanity. 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 that would be impossible even for elite units.

Crisis (2534-2535)


With majorities of the Outer Colonies glassed or abandoned, the UNSC faced an economic crisis as some of their Agriculture Worlds had been destroyed, leading to food shortages. On Charybdis IX, food 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". It stated that no UNSC vessel may 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 saw as a removal of their right to freedom of movement. Another development was the discovery of Insurrectionists using Covenant weapons modified for human use. The UNSC saw this as a threat to security as the weapons may have been carrying Covenant homing beacons. The Covenant saw it as heresy that humans would modify their weapons, and the Prophet of Regret dispatched Thel 'Vadamee to destroy the source of the modified weapons: The Rubble.

Fleeing from the Battle of Charybdis IX, the chased an Insurrectionist freighter to the Rubble and discovered that the Insurrectionists there had actually formed an alliance with a colony of Kig-Yar. The Jackals were supplying the weapons and the Insurrectionists were modifying them. The crew of the Midsummer Night, including its captain, Lieutenant Jacob Keyes, were captured, but later escaped and helped 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 of 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)
For fifteen years, the war continued in much the same way as before; minor, costly victories on the ground for UNSC forces, but 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, the loss of its colonies at Leonis Minoris, and the total destruction of the force of SPARTAN-IIIs sent 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, and the Second Battle of Arcadia and the loss of Paris IV in 2549. One of the UNSC's success was Operation: TORPEDO in 2545, and even then it was a Pyrrhic victory at best.

Of the few wins in the 2540's for the UNSC, one of the most significant, and strategically advantageous, 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 the Unyielding Hierophant and the actions of Spartan-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 on Sydney, Earth.

Towards what appeared to be the obvious end of the war by 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.

The Final Year (2552)
The last year of the war saw humanity's largest defeat since the war's beginning, 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 Cote d'Azur. However, in space, the Covenant placed a Spy Probe on the UNSC Iroquois, which led the Covenant to the UNSC's stronghold and main headquarters, Reach.

The Battle of Reach that followed had staggering losses for both sides, but ended in a Pyrrhic Covenant victory. The Pillar of Autumn was among the surviving UNSC ships which fled the battle, and made a somewhat blind jump, as described by Cortana saying that she realized that the symbols on the retrieved artifact from Sigma Octanus IV were in fact very old star charts and were coordinates to the Forerunner ring world of Halo, being chased by a dozen Covenant warships.

The Tide Turns (2552-2553)


The Covenant's first costly defeat was on and around Installation 04. Here, the Human survivors from the Halcyon-class cruiser, the Pillar of Autumn, managed to form an effective and surprising resistance to the Covenant. Unwilling to risk damaging the sacred ring, the Covenant was forced to fight the Humans on Halo's surface rather than using its usual bombardment tactics. The Covenant found the Humans uncannily adapted to Halo's environment and very adept at fighting on the surface, with Human firearms and vehicles proving effective despite their technological inferiority. Unable to counter the guerrilla tactics employed by the Humans, the Covenant was soundly defeated in numerous raids, including one instance when the 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 the Master Chief 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 horrified dismay. 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.



Shortly after the defeat at Halo, the Covenant had amassed a large fleet that appeared to be intended to assault Earth. 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, the 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 to be intending to assault Earth; 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 the Human homeworld. The surviving Humans, however, believed this fleet to be a direct threat to Earth, and, using a captured Covenant flagship, lured the fleet 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, supposedly 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, but a counter-attack by the Marines and John-117 drove them back. With his fleet destroyed in orbit when he landed, Regret was forced to retreat. His carrier jumped into Slipspace from within the city, damaging it severely.

Unfortunately for Regret, four Human ships, the In Amber Clad among them, had followed them through their own Slipspace rupture to Delta Halo. With the orders "Find out why he came to Earth; why he came here," the Master Chief was hard-dropped with a complement of Orbital Drop Shock Troopers to Delta Halo's surface. Led by the Chief, 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 the plan to remove the Sangheili from power in the Covenant. The Chief killed Regret. The Prophet of Truth then gave the order to glass the temple in which Regret was residing. It seemed as though Master Chief was eliminated. In fact the Chief narrowly avoided being glassed, only to be captured by the Gravemind.



Meanwhile, the majority of the Human forces on In Amber Clad had traveled to Delta Halo's Library to obtain the Index, which is the key to firing Halo. Originally, the Covenant had been unaware of the Index's importance, but luckily for them, 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. Just as Miranda Keyes claimed the index, the Arbiter stole it from her, kidnapping her and Sgt. Johnson. However, then Index was stolen from the Arbiter by the Brute Chieftain Tartarus, who was under the Prophets' orders to retrieve the Index and kill the Arbiter, whom Tartarus knocked down an apparently bottomless shaft. With the Index secure, the Prophets then ordered the Jiralhanae to begin eradicating the Sangheili, thus starting the Covenant Civil War. Ultimately this led to the death of Tartarus at the hands of Vadamee and Johnson and an alliance between the Separatists and the Human forces. Delta Halo was prevented from firing by Miranda Keyes and the Flood killed the Prophet of Mercy, leaving the Prophet of Truth firmly in control over the Covenant.

The Battle of Onyx


Long before the events around Halo, the classified UNSC 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. After Blue Team made landfall, Fleet Master Voro Nar 'Mantakree's fleet arrived at Onyx, taking down hundreds of orbiting Sentinels before discovering the UNSC forces in the recently-uncovered Forerunner city below. 'Mantakree personally led the Covenant forces on the surface, before the UNSC Battlegroup Stalingrad arrived and used tactical skill and 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 two FENRIS Nuclear Warheads, killing the entire Separatist force. Following the Core being sealed, Onyx broke up into trillions of Sentinels, guarding the construct.

Arrival of the Flood and Sangheili/Human Victory (2552-2553)
"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 much fighting, the Human forces on Earth on the naval side had taken heavy casualties. However, the Covenant 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.

However, Truth quickly activated a large portal and escaped. Events were further complicated by an unexpected attack by the Flood. Thanks to the timely arrival of the Elites, 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 Elite 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 Human/Elite fleet was outnumbered 3-1, the battle ended in defeat for the Covenant Loyalist Fleet. Simultaneous to the 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 November 2552 as Truth attempted to activate the Halo rings. Led by the Master Chief, the Human forces smashed through the remaining Covenant resistance on the ground. The battle was complicated by the arrival of High Charity. As the Flood began to spread, the Chief and the Arbiter went on to thwart Truth, who died in mid-Flood-infection at the Arbiter's hand with the Flood helping to reach him. 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 Seargeant Johnson by firing the Halo over the Ark, destroying both, but John-117 was presumed dead afterwards as he never made it back to Earth.



Some months later, in March 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 Spartan-117's name was included as he was presumed MIA by the UNSC, as no Spartan could be declared dead. Lord Hood shook hands with the Arbiter to signify an end to hostilities. Both sides then started rebuilding all the damage the war had cost.

United Nations Space Command
Leaders: HIGHCOM

Homeworld: Earth (largely intact at the end of the war, with the exception of a section of eastern Africa which was glassed)

Military Forces: Unknown, possibly in the hundreds of millions.

The Covenant
Leaders: The High Council

Homeworld: multiple worlds - different member races.

Capital City: High Charity (destroyed by John-117 after it was turned into a Flood Hive and crashed on the Ark)

Military Forces: Exact numbers are unknown, but much larger than Humanity's forces.

The Flood
Leaders: The Gravemind (destroyed when John-117 and Cortana fired Halo)

Homeworld: Unknown, extra-galactic.

Military Forces: Believed to be massive; probably into the trillions.

Remaining Forerunner Constructs
Leaders: Unknown, Forerunner AI including monitors such as 343 Guilty Spark.

Homeworld: Created on most constructs.

Military Forces: Sentinel count believed to be in the tens of trillions (there are multiple Shield Worlds and Onyx alone was composed of "trillions").

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 Jackal 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. Afterwards, the Minister of Fortitude becomes the Prophet of Truth and declares war on Humanity.


 * Shortly after the attack on Harvest, the colonies of Green Hills and Second Base are glassed.


 * The Battle of Chi Ceti takes place.

2526

 * 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 2/3s 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 Covanant almost 10-1, but lost a third of the ships. This was one of the rare naval "victories" for the UNSC

2528

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

2530

 * The Covenant destroys the UNSC colony world of Eridanus II
 * Battle of Groombridge-1830, 11 UNSC Destroyers are lost 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.
 * First Battle of Arcadia
 * Battle of the Flood-controlled Shield World
 * Battle of the Apex
 * 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.

2535

 * Battle of Charybdis IX
 * Battle of the Rubble
 * The Covenant destroys the UNSC colony world of Jericho VII in the Battle of Jericho VII.
 * 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 Colony worlds 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 killed 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 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 destroyed in the battle.

2545

 * Operation: TORPEDO: UNSC Victory. All SPARTAN IIIs, with the exception of Tom-B292 and Lucy-B091 of SPARTAN-III Beta Company are killed by Covenant forces.

2547

 * The UNSC colony of Skopje is destroyed by the Covenant.

2549

 * Siege of Paris IV, Covenant victory.
 * Second Battle of Arcadia, Covenant victory, Arcadia is glassed.

July

 * 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 Grunts and Jackals.


 * 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.

August

 * Battle of Reach. 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. The UNSC Pillar of Autumn escapes.
 * Battle of Tribute

September

 * Battle of Installation 04. The 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.


 * 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 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 Prophet of Regret's Assault Carrier 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, the UNSC In Amber Clad, arrives in time to participate in the battle. Again, released Flood and Forerunner overseers join the struggle. The Prophet of Regret is assassinated by John-117. Again, the installation is prevented from firing and the Flood appear to take control of the installation.


 * The Civil War of the Covenant begins. Covenant forces are thoroughly divided between the Elites and the Brutes. Every race in the Covenant takes sides. The Prophet of Mercy is later killed by a Flood Infection Form. High Charity itself is eventually overrun by the Flood infestation.


 * 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, the Bloodied Spirit, to relieve Onyx. Covenant and UNSC ships converge on Onyx but ultimately all are destroyed except for the 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 Separatists, pushed back the Loyalist invaders.

Late 2552

 * Battle of Installation 00.
 * All Loyalist vessels are destroyed over the Ark by the Separatist Fleet.
 * The final Covenant religious leader, the Prophet of Truth, is executed by the Arbiter with help from the Flood. The Master Chief stops the Ark from firing the Halo Rings.
 * High Charity is destroyed by the Master Chief after he blasts the city's main reactors causing them to go critical.
 * The Battle of Installation 04 (II). Thel 'Vadam, John-117 and Johnson battle to the control room that's on Installation 04 (II). Guilty Spark runs rampant, killing Johnson before being destroyed. Installation 04B’s Sentinels turned on John-117 and Thel 'Vadam. The unfinished Installation 04 is activated, damaging the Ark and destroying the entire Flood infestation including the Gravemind. These final events ended The Human-Covenant War. However, the Dawn is torn in half while entering the portal home, sending 'Vadam to Earth, but leaving John and Cortana lost in space.

December

 * The Arbiter returns to Earth in the frontal half of Forward Unto Dawn, crashing into the ocean. He is safely cut out of the wreckage by UNSC forces.

March

 * While the fighting finished in December, hostilities were not ceased officially 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.

Trivia

 * The very first Covenant species to encounter the Humans were the Unggoy, the Huragok, the Kig-Yar, and the Jiralhanae, - in that order - all prior to the inception of the war.
 * The first known human casualty that the Covenant inflicted, was Henry "Hank" Gibson, pilot of the freighter This End Up, when a Huragok named Lighter Than Some threw a hunting rock into his head to protect its Unggoy friend, Dadab. Hank had been assaulting the Unggoy, believing Dadab to be one of the aggressive boarders - the Kig-Yar.
 * The first Covenant alien killed is the Kig-Yar, Zhar, who is killed by Staff Sergeant Avery Junior Johnson.
 * Sergeant Johnson fought in both the first and last battles of the war, and is the first to kill a Covenant warrior and witnesses the final blow of the war when the Arbiter kills the Prophet of Truth.
 * Sergeant Johnson was the only human to witness both the beginning and end of the Human-Covenant War as he was present when Harvest was attacked, and saw Truth killed, which signified the end of the war.
 * The nickname of the Human-Covenant War (the Great War) is the original name of World War I.
 * The Minor Transgression was the first Covenant ship to be destroyed in the war.