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 between the United Earth Government and its United Nations Space Command and the Covenant empire during the mid-26th century between October 7, 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.

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 and technology, overpowered humanity on hundreds of worlds, including heavily defended strongholds such as Reach. Humans only won 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 and Flood, and the official cessation of hostilities on March 3, 2553. The war was incredibly costly to both sides, with billions of humans and likely hundreds of millions of Covenant killed during the hostilities and and further heavy causalties during the Flood plague.

Declaration of War (2525)
Humanity and the Covenant first came into direct contact in 2525, when a Covenant Frigate, under the misguidance by Truth and other prophets, that the Humans were hiding Forerunner artifacts, attacked the UNSC Outer Colony world Harvest. After several encounters (Including the Covenant's raiding of several UNSC supply ships and a minor skirmish between Staff Sergeants Nolan Byrne and Avery Johnson against Kig-Yar privateers), the UNSC and Covenant officially met on Harvest in a diplomatic meeting, although rather than peace, the Covenant was only interested in claiming the planet due to the number of supposed Forerunner artifacts within it, with or without the Humans' immediate surrender. The meeting was botched after Osmo, a member of the Colonial Militia, was attacked by a nervous Grunt, a member of a second Covenant force attempting to stage an ambush of their own, and a firefight erupted.

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 all the Humans was partly a religious issue and partly an attempt by the Prophets to keep their power. The Prophets found out that the Forerunner objects that the Luminary was picking up on Harvest were actually Humans (which the Prophets interpreted as meaning that the Humans were descendants of the Forerunner, or possibly surviving Forerunner). At first they interpreted it as "Reclamation". Mendicant Bias, a Forerunner AI (accidentally found) told that the interpretation was wrong and it meant "Reclaimer". The Prophets (mainly Regret and Truth) realized that that meant that it was possible to destroy the belief of the Great Journey as they see humans as inferior beings, and if human and forerunner are the same thing that would mean forerunner are inferior and they may have to worship humans, and they may lose their power. They agreed that if the rest of the Covenant discovered this, they would cease to follow the Prophets and defect to Humanity. The Prophets then decided to wipe out the Human race to hide the truth that it was possible to be left behind on the Great Journey from the rest of the Covenant.

An example being the extended, though one-sided, ground battle which took place on Harvest, where the Humans successfully halted the Covenant for some time, but the Covenant eventually used their capital ships' plasma weaponry, to melt the planet's surface, a process which would become known as "glassing."

Open War (2525-2552)
From that point on, the Covenant continued to attack and destroy the Humans wherever 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 planet-side, 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 missile, 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 before the Covenant counterattacked again at Harvest in 2531.

The Apex and the Arbiter (2531)
Despite their major numerical and technological advantages over humanity, by 2531, the Covenant High Prophets had realised 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 Ripa 'Moramee to Harvest to claim a Forerunner artifact buried under the north pole.

Preston Cole counterattacked by leading a fleet composed of the and the  back to Harvest after receiving a message from an ONI Prowler. The Third Battle of Harvest 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 realised 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 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. Whether Arcadia contained more Forerunner artifacts that the Covenant wished to claim, or they had simply followed the map in order to destroy another human colony, is unknown.

The crew of the Spirit of Fire eventually discovered that the Covenant needed the researcher 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 Apex.

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. SPARTAN-III Alpha Company was created in 2532 and Beta Company in 2541. However, their stated goal of destroying high-priority targets often led to near-total losses during assaults on the Covenant. Alpha Company was totally destroyed on K7-49 during Operation: PROMETHEUS in 2537, while Beta Company was wiped out with only two survivors in Operation: TORPEDO in 2545. ONI considered the gains to outweigh the losses and SPARTAN-III Gamma Company was activated in 2551.

Crisis (2534-2535)
With most of the Outer Colonies glassed or abandoned, the UNSC faced an economic crisis as most 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 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 Fall of Arcadia and the loss of Paris IV in 2549. The UNSC's one success was Operation: TORPEDO in 2545, and even then it was a pyrrhic victory at best. 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 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 known truly 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 resistance. 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 and the unexpected emergence of the Flood, 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. During the course of the battle, the Spartan known as the Master Chief discovered the true nature of Halo and proceeded to destroy the ring and escape, 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 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 a 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 counterattack by the Marines and the Master Chief 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, destroying it and clearing the area for a later Covenant excavation of the Ark, though the latter consequence was probably unintentional.

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 compliment 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, but they were too late. The Chief assaulted and killed Regret, and the Covenant Fleet recalled the Phantoms in favor of bombarding the area. It would seem they succeeded in "killing" Master Chief by burning away the building, as he came inches away from getting incinerated by the massive plasma beam glassing the area, plummeting down into the lake below, 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 from the first Halo 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 Brutes to begin eradicating the Elites, thus starting the Covenant Civil War.

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 honours exercise on the surface. After the humans failed to exchange the proper counter-responses, the Sentinels relabled the "Reclaimers" as aboriginal subspecies and began to exterminate them. Led by Kurt-051, the SPARTAN-IIIs fought a guerilla 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 (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 Spartan 117 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 the Master Chief, the humans 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 Loyalists. During the space battle, Human 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. 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 Covenant forces completely shattered, Truth's death marked the effective end to the war.

A year later, in 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 was presumed dead by the UNSC. However, John and Cortana weren't dead. They had survived the firing of Halo as the aft section of the UNSC Forward Unto Dawn entered the portal. However, the portal had collapsed whilst still traveling through it and the aft section was sent to an unknown location far away.

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: 200 million

The Covenant
Leaders: The High Council

Homeworld: multiple worlds - different member races.

Capital City: High Charity (destroyed by the Master Chief 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

Homeworld: Unknown

Military Forces: Believed to be Massive, possibly into the billions or 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 trillions

2524

 * 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. 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.
 * After the First Battle of Harvest, the Minister of Fortitude becomes the Prophet of Truth and declares war on Humanity.
 * 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.

2530

 * The Covenant destroys the UNSC colony world of Eridanus II.

2531

 * Third Battle of Harvest
 * First Battle of Arcadia
 * Battle of the Flood-controlled Shield World
 * Battle of the Apex

2534

 * Battle of Charybdis IX
 * Battle of the Rubble

2535

 * 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.
 * 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.

2544

 * Spartan-II super soldier Sheila dies in the Battle of Miridem.

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.

2549

 * Siege of Paris IV, Covenant victory.

July

 * Battle of Draco III. Covenant kill all UNSC ground forces and capture 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

 * First Battle of Reach. 314 Covenant ships destroy 152 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.

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.
 * Second Battle 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 rout and destroy a fleet of 500 Covenant starships 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

 * First Battle of Earth. 15 Covenant ships assault Earth, defended by at least 75 or more UNSC vessels 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.

November

 * Battle of Installation 05. The lone surviving Covenant warship from the First Battle of Earth retreats to Installation 05, pursued by a score of 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 SPARTAN-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.

Late 2552 to Early 2553

 * Second Battle of Earth. The Brute faction of the Covenant returns to Earth in force, apparently conquering Africa. Later, during the next few months Marines, with help of the Separatists, pushed back the Loyalist invaders.
 * Battle of Installation 00.
 * All Loyalist vessels 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, Master Chief and Johnson battle to the control room that's on Installation 04 (II). Guilty Spark runs rampant, killing Johnson before being destroyed. Alpha Halo’s Sentinels turned on the Master Chief, Thel 'Vadam, and the Elites. 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.
 * The Master Chief, Cortana, and Thel 'Vadam escape but only Thel 'Vadam gets back to Earth. The Master Chief and Cortana are drifting in between Earth and The Ark due to the portal closing. They are inside the back half of Forward Unto Dawn, and no one on Earth knows what happened to them.

March

 * The war ends in a UNSC-Covenant Separatists victory. The victors erect a monument on a hillside near the Ark's Gateway to commemorate those fallen. At this time John-117 and Cortana are declared MIA.(They are shown to be alive floating towards a currently unknown planet.) 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 war actually started at Harvest, where the Brute ship Rapid Conversion attempted to recover the Forerunner relics that had been revealed by the ships Luminary.
 * 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 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 where the Arbiter kills the Prophet of Truth.