Halo universe

"Halo is an epic journey to save humanity from a terrible menace."

- Chris Carney on Halo 3 Legendary Edition: 7 Steps To World Domination

The Halo universe is the sprawling fictional universe in which all Halo media takes place. Encompassing hundreds of millennia, most of Halo ' s central events are set in the 26th century of the Gregorian calendar, with humankind colonizing the galaxy only to stumble upon a hostile alliance of aliens known as the Covenant, who, motivated by the power of the Prophets and the promises of paradise after death, are bent on humanity's destruction.

It is this universe where the Halo video game series: Halo: Combat Evolved, Halo 2, Halo 3, Halo 3: ODST, Halo Wars, Halo: Reach, Halo 4, and Halo: Combat Evolved Anniversary take place. In addition to the games, a number of Halo novels and other media including comic books, short films and an anime collection have been released. The media beyond the game series expands into the Halo universe timeline before and after the events of the games, as well as running concurrently with the games' timeline.

Primary factions
In the Halo universe, there are lots factions, political groups, races, planets and species. The main factions are as follows:

United Nations Space Command


In the 26th century, most of humanity is ruled by the United Nations Space Command (UNSC). As most of the material from the Halo universe is from the ongoing war we see the future mainly through the eyes of the UNSC's military arm called the United Nations Space Command Defense Force (UNSCDF). During the events of Halo 2 and Halo 3, the UNSCDF fought the Covenant over Earth in a last-ditch attempt to protect the human race. The events of Halo: Reach are fought defending the planet Reach, the UNSC's military headquarters.

The UNSC was formed by the United Nations when overpopulation on Earth and conflict in the Sol System started becoming a severe problem in the early 22nd century. In the wake of the conflicts in the 2160's, the UNSC became the military and space exploratory arm of the newly-established Unified Earth Government (UEG). Due to the emergence of the Covenant threat, the UNSC has been given power over the UEG and its colonial governing agency, Colonial Administration Authority.

Run by HIGHCOM, the UNSC is Earth's premiere defense against the Covenant. The Navy houses the divisions of Marines (including the Orbital Drop Shock Troopers), the Office of Naval Intelligence (ONI), and the fleet. Originally designed to keep the peace between neighboring planets and star systems, when certain rebellious factions began to present a problem in the late 2490s, the UNSC was forced to police its colonies to keep privateers and pirates from raiding them.

There are several breakaway factions opposed to UNSC and the Colonial Administration Authority as well, including the United Rebel Front.

The Covenant


Originally formed by as an alliance between two species; the Prophets (San 'Shyuum) and the Elites (Sangheili), the Covenant is a theocratic hegemony of multiple alien species. The name "Covenant" is based on the "binding Covenant" formed between the two races, when the Sangheili promised to defend the San 'Shyuum as they searched for the "Sacred Rings" (Halo Array) which are said to start the "Great Journey", a term that the Prophets use to explain the disappearance of their Gods, the Forerunner race. The quest of the entire Covenant, the Great Journey is the basis of all of their worship. As the Covenant Empire grew over a millennium, more species were enslaved to their cause, although, up until the Great Schism, none of them were quite as important to the Prophets as the Elites.

At first, the Covenant were mostly held together by a need to survive, but as their society advanced, so did their technology, culture and religion. Now the polytheistic Covenant control a large part of the Orion arm of the Milky Way galaxy and their society is a complicated caste system, with the Prophets still on top, governing the Covenant along with the Elites. The Covenant is a theocracy, based on a prophecy about the Sacred Rings and the Great Journey. The actual context of this prophecy is based on the notion that the Forerunners were so advanced that they had found a way to propel themselves to godlike status using their technology. To oppose this, a parasitic race known as the Flood attacked the Forerunners and attempted to stop the activation of this technology. Before the Flood could stop them, the Forerunners activated the Halo array, and ascended to godhood. The Covenant design is to find the Halo array, and use it to propel themselves to godliness as well.

The three leading Prophets, the Hierarchs of the Covenant, want to destroy humanity due to the threat they pose to their religion: if humankind really are the Forerunners' heirs, then all that the Covenant believe in is false. Not wanting the truth about the humans to get out, the rest of the Covenant have been told that humanity is a direct affront to the Forerunner, much like the Flood in goal, so must be exterminated if the Great Journey is to be completed.

The Flood


The Flood (called The Parasite by the Covenant) is a species of virulent, parasitic organisms that thrive by consuming other sentient life of sufficient biomass, no matter where in the universe, thus leading Forerunners to the creation of the Halo Array. The Flood appears to be a hive or communal mind, existing in several stages that eventually lead into the creation of a central intelligence known as the Gravemind.

The Flood grow and reproduce via the assimilation of other beings, utilising corpses and acquiring any biomass (including both animal and plant) in order to spread. They are incapable of sexual reproduction, instead they fester inside a host until a certain time period, after which they explode and many new Flood are given off. Once a Gravemind is formed however, the Flood advance to a stage where they no longer require hosts for this, only biomass and calcium, which they require to feed on, and to build bodies with. Once they have advanced, they create hives which can produce thousands of Flood inside large pustules on walls and other surfaces, which act as incubators. During this stage, the Flood are able to build their own life forms using captured biomass and calcium deposits. The Flood continue in this fashion recurrently until either everything is devoured, or until they are stopped, the former usually occurring.

Next to nothing is known about their origin, except that they arrived from another galaxy through unknown means, and fought both prehistoric humans and Forerunners, eventually defeating the latter. The Forerunners discovered and then fought them until they were overwhelmed after centuries of war. Faced with the Flood spreading throughout the galaxy and consuming every sentient being, the Forerunners created seven artificial rings called the Halos, large "fortress worlds" in the shape of rings, to contain and hopefully stop the Flood from ever spreading. The point of the rings was to wipe out all sentient life, thus starving the Flood of the sufficient biomass required for them to continue spreading. Through their own interpretation of Forerunner artifacts, the Covenant believed these rings were actually devices that allowed the Forerunner to transcend this plane of existence into godlike state, and thus they seek to do the same by activating them once more, not realising they would inadvertently wipe out all sentient life in the galaxy if they were to be successful in doing so.

Although it seemed the plan had been successful at eliminating the Flood threat, samples of the organism kept on the rings for study were released on at least two of the installations through accidental means, putting the Galaxy once again at risk of complete destruction by the parasite.

The Forerunners


Once the dominant civilization in the Milky Way, the Forerunners reached unparalleled technological advancement over 110,000 years before the Human-Covenant War. Apparently charged by the mysterious Precursors with protecting less advanced civilizations in the galaxy, they stumbled upon the Flood and fought a three-hundred-year long war to stop the genocidal parasitic species from overrunning the galaxy. When it looked as if they were going to fail at that task, they built and activated the Halo Array - sterilizing the entire galaxy of sentient life including themselves, starving the Flood into submission, and repopulating the galaxy again with those few species saved from extinction.

All that remains now of the Forerunners are the ruins of their ancient temples and cities, a few scattered pieces of functional technology, and their automated combat and maintenance constructs. Their technological brilliance, combined with a garbled version of the Halo activation, led to the Covenant's religion revering the Forerunners as deities, and that this state could be achieved again by activating the Halo's. In turn, these attempts led to the Human-Covenant War, and the eventual secession of the Sangheili and their alliance with humanity to stop the Covenant.

Transport

 * Slipspace, used by both the Covenant and UNSC, is the primary method of faster than light travel in the Halo universe. A Forerunner crystal captured at Reach allowed for manipulation of space-time and Slipspace, dramatically shortening the length of travel time through Slipspace and allowing exit from the ship whilst in Slipspace. Humans have not exacted the science of Slipspace jumping, and can often end up hundreds of thousands of miles away from where they want to be, and therefore they work to be inexact, so as not to end up somewhere like the middle of a planet. The Covenant had worked a way around this, as they can pinpoint jump anywhere in the galaxy, even maintaining their formation. The UNSC fears this, and that is why they have to keep the location of Earth so secret.
 * The Forerunners developed teleportation technology, allowing near-instantaneous transit over short distances.
 * Wheeled contrivances similar in appearance to today's vehicles are used by the UNSC. However, the Covenant prefer to use hovering technology assumed to be based on Forerunner technology.

Artificial intelligence

 * AIs, some of which are modeled after a human brain, work at superior speeds and with greater efficiency; helping with astronavigation, maintenance, managing, and even battle.
 * Standard AIs are incredibly intelligent within their programmed fields whether that be battle strategy, or maintaining plantations on Human colonies.
 * Smart AIs are brilliant and have no limit to their imagination or intelligence other than that of their maximum storage capacity. However, they have a limited lifespan of seven years before they go mad, or "rampant".
 * The Covenant refer to AIs as Associated Intelligences.

Weapons and armor

 * While the UNSC still uses conventional weapons to a great degree, several innovations have been made. Standard armament on UNSC warships includes both conventional and nuclear missiles, guns of varying sizes, and perhaps most notably, the Magnetic Accelerator Cannon, a type of coilgun capable of delivering metallic projectiles at immense speeds. The UNSC also possesses a handful of directed energy weapons, including the man-portable M6 G/GNR anti-vehicle laser.
 * Most Covenant weapons are plasma-based, from their starship weapons to the smallest infantry arms. Several laser-based weapons are also in use, as well as weapons whose methods of operation are wholly unknown.
 * Energy shielding technology, originally developed by the Forerunners, is featured on most Covenant starships, installations and is integrated in some infantry armor systems as well. During their war with the Covenant, the UNSC have reverse-engineered this technology, though its applications are nowhere near as widespread as in the Covenant.

Other

 * Artificial gravity is common on both UNSC and Covenant starships. While some UNSC vessels possess rotating centrifuges to enable this, both factions have developed technology capable of generating artificial gravity though some unknown mechanism. Anti-gravity technology is also used by both factions on their starships, allowing them to descend and hover in a planet's atmosphere.

Prehistory
Millions of years before the rise of the Forerunners, an advanced civilization known as the Precursors controlled the galaxy. Having reached the pinnacle of technological advancement, they were believed to have affected the evolution of life in the galaxy, even created the species known as Forerunners, but later they would be wiped out by the Forerunners millions of years before the emergence of the Flood.

Approximately 150,000 BCE, having mastered interstellar travel, humanity, still composed of many species, arose from their homeworld Earth, known as "Erde-Tyrene" at the time. They began to move their civilization along the Orion Arm of the Milky Way galaxy, to escape Forerunner control. They allied with the San 'Shyuum species, forming a prosperous interstellar empire based on the planet Charum Hakkor. Later, the humans stumbled upon starships of unknown origin near the edge of the galaxy. These vessels contained fine powder that proved to have supposedly beneficial psychotropic effects on animals, such as the Pheru, favored by humans as pets. However, over the following centuries, the use of the powder began to mutate the Pheru, spawning irregular protrusions and growths and eventually altering their behavior.

Eventually, humans and San 'Shyuum became infected by the disease, actually an early stage of Flood infestation. Hundreds of systems were lost to the parasite in a conflict between the humans and the Flood. Meanwhile, humanity's aggressive expansion and the perceived violations of the Mantle prompted the Forerunners to take action and begin a war against humanity. Despite being forced to fight a two-front war against the Flood and the Forerunners, humanity eventually drove the Flood out of the galaxy. However, the Forerunners eventually emerged victorious over humanity after defeating their last stronghold on Charum Hakkor.

Following the war in approximately 109,000 BCE, the Forerunners dismantled humanity's civilization, regressing them into a Tier 7 species. The remaining humans exiled to their homeworld Earth, where a Forerunner Lifeshaper, the Librarian established a research station. In the following millennia, the Librarian would tend to the humans, eventually allowing their civilization to begin developing anew.

Circa 100,300 BCE, the Flood would resurface on worlds resettled by the Forerunners after the human-Forerunner wars. For three hundred years, the parasite would claim Forerunner planets across the galaxy. As a final resort, the Forerunners fired the Halo Array, a superweapon which eradicated all neurologically complex life in the galaxy and subsequently caused most Flood to die out. While life was re-seeded into the galaxy by Forerunner automatons, the Forerunners themselves would not return, passing their "mantle" to humanity.

Rise of the Covenant
Dozens of millennia after the disappearance of the Forerunners, two original species of the Covenant, the San 'Shyuum and the Sangheili, spent years locked in a bitter war over the control of the remains of the Forerunners. The Prophets wished to use the technology to search and explore the galaxy, but the Elites believed such usage to be a desecration of their holy artifacts. As the devastating war ravaged both species, the Elites saw that the only way for them to win was to do the exact thing they opposed; use their own Forerunner technology to adapt and befit their vessels. Eventually, the two species formed an alliance which was formalized with the Writ of Union. Over the following centuries, many species would be absorbed under the power of the Covenant hegemony, and thus conscripted into the search for Forerunner relics, and later the attempt to eradicate the human race.

Origin of the UNSC
In the late 21st and early 22nd centuries, humanity colonized several worlds in the Sol System, including Earth's moon, Mars, the Jovian Moons, and several asteroids. In the years 2160-2200, various governments and factions fought for control of Earth and its first colonies. As overpopulation and unrest on Earth mounted, new political movements formed including the Jovian Frieden and Koslovics led by Vladimir Koslov, resurgences of fascism and neo-communism which waged the Interplanetary, Rain Forest Wars and Mars clashes and were defeated by the victorious United Nations Space Command. The Unified Earth Government was established following the conflicts, emerging as the rulers of most of humanity who now faced the problem of overpopulation, famine and economic instability caused by the wars.

In the late 23rd century, humanity developed the Shaw-Fujikawa Translight Engine, a device which enabled faster-than-light travel through a domain of alternate space-time known as slipstream space. The first extrasolar colony ships went on to colonize worlds in nearby systems within the next decades. The Inner Colonies, as they later came to be known, would be considered the elite, in contrast to the more remote and less wealthy Outer Colonies, formed over the course of the 2400's.

In the 2490's, with over 800 settled worlds across the Orion Arm of the Milky Way galaxy, humanity's "Golden Age" of expansion was coming to an end. Gradually, the Outer Colonies had became more isolated and unstable. Their populations had widely varying loyalties to Earth, and taxes and trade restrictions set up by the UEG's colonial governing agencies caused dissent against the Earth government. This eventually led to the Insurrection, an undeclared civil war between the UNSC and the various rebel groups that rose up against it in the Outer Colonies.

Insurrection and the SPARTAN-II Project
By 2517, the UNSC was facing extremely low morale due to piracy and the ongoing Insurrection. In order to remove the rebellion without a significant sacrifice of human life, Dr. Catherine Halsey decided to move forward with the SPARTAN-II project. 75 physically and mentally gifted children were abducted at the age of 6, replaced by flash-clones in a UNSC black-op, and drafted into the UNSC. The children went through rigorous training and physical augmentations through surgical and medicational means. Code-named 'SPARTANs', this project genetically enhanced troopers were trained for a life of battle, and would become a great asset against the Covenant in both frontline and covert operations; the Spartans specialising in both.

The Human-Covenant War begins
On February 3, 2525 the UNSC colony of Harvest detected an unknown object on its long-range radar. The object was constructed with materials unlike anything seen before. All contact with Harvest was lost soon after. Ships sent to the system revealed that it had been totally destroyed by a new alien group called the Covenant. A battle group was sent but was defeated by the military superior Covenant ships. Only one ship made it back, the returned with a message that was sent to them, pre-translated, saying, "Your destruction is the will of the gods, and we are their instrument".

In response, Vice Admiral Preston Cole mobilized the largest space fleet in Human history to retake Harvest. The fleet defeated the Covenant ships at Harvest in 2531 but at great cost with Cole losing two-thirds of his fleet. The highly advanced Covenant shielding and weapons systems simply outclassed anything they had and so began the slow destruction of the Human race. One by one the UNSC colonies were lost until by 2535, virtually all of the Outer Colony worlds had been destroyed by the Covenant and the Inner Colonies were being invaded. The Cole Protocol was established by military order: all human vessels must ensure that Covenant forces do not find Earth. To achieve this whenever they must jump out of a battle, they must do so to a randomized vector that points away from any human worlds.



Fall of Reach
By 2552, many of humanity's Inner Colonies had been destroyed by the Covenant. The UNSC leadership assembled a Spartan II strike team, at the human command base on the planet Reach. In a move of desperation, the UNSC planned to launch a targeted strike against the Covenant leadership. This plan was abandoned when the Covenant launched a surprise attack on the world of Reach.

During this battle, most of Reach is overrun and glassed, and the human fleet obliterated. One of the Spartans, John-117, is able to escape on the ship Pillar of Autumn along with her crew. In fleeing the Covenant fleet, the POA onboard AI, Cortana, uses some coordinates from a recently discovered Forerunner artifact that leads them straight to the Forerunner's Installation 04.



Alpha Halo


Three weeks after escaping Reach, the Pillar of Autumn exits Slipspace to find a mysterious ring shaped space station orbiting the gas giant Threshold. The ring, referred to by the Covenant as "Halo", is an artificial construct that is teeming with life. A Covenant fleet, however, is also present, and a subsequent battle heavily damages the Pillar of Autumn and the ship crash lands onto Halo.

The first Halo game begins in earnest with the Master Chief's escape from the Autumn, and continues upon landing. The first levels of the game deal with an attempt to reach Halo's control center to uncover its purpose. It is soon discovered that the Covenant have accidentally released "The Flood", a parasitic alien species. The Flood then sweep across Halo and devastate Human and Covenant forces positioned on it. The release of the Flood prompts 343 Guilty Spark, an eccentric Forerunner A.I., to try to activate Halo's defense system, a pulse weapon that, when fired, would wipe out all sentient life in the galaxy large enough to be hosts for the Flood. Technically, that installation only has a maximum effective radius of 25,000 light years, but the pulse would trigger other installations as well, effectively killing all intelligent life in the galaxy. This system is designed to stop the Flood from spreading through the universe if they escape confinement from Halo by the only way possible: starving the Flood of any life source that can sustain them.

Naturally, this would wipe out Humanity as well, and so the final levels of the game revolve around the Master Chief's attempts to destroy Halo before it fires by self-destructing the POA. Despite the abuse sustained during the space battle and the following crash the Pillar of Autumn remained intact, and was subsequently occupied by investigating Covenant forces and later by Flood.

Having manually triggered a destabilization of the power cores the Master Chief and Cortana commandeered a Longsword from one of the Pillar of Autumn's docking bays and achieved a safe minimum distance before the ship exploded, causing the ring-world to fragment.



Operation: First Strike
Occurring between Halo: Combat Evolved and Halo 2, Halo: First Strike starts off with Master Chief and a few other survivors in space above the destroyed Halo. They capture a Covenant flagship and make their way back to Reach. When they arrive they find the entire planet ravaged. Yet something is strange. The Covenant usually glass a world and move on, but there are small patches of the planet left unscathed. It is discovered that other Spartans who survived the fall of Reach have found a Forerunner structure under ONI's CASTLE Base. There they find a special artifact that warps space-time.

Cortana, now in control of the Covenant ship, docks with a partially destroyed UNSC ship and combines their power (and also to allow them to return to Earth without violating the Cole Protocol by bringing a potentially "bugged" Covenant ship with them). After toying around with the controls she realizes that the Covenant know virtually nothing about the technology they possess. She reconfigures the plasma turrets to fire more effectively, increasing their destructive power. She also finds out how the Covenant moves so easily through Slipspace. The technology she gathers could effectively turn the tide of the war.

After going through many battles the Master Chief and other Spartans discover a massive plot to attack Earth. They covertly attack and destroy a massive Covenant refit and repair station along with an attack force many times larger than the one that attacked Reach. In doing so they lose the Covenant flagship; however, they save the UNSC ship and escape back to Earth with it. Thus, begins Halo 2.

Delta Halo


Halo 2 starts with the beginning of a Covenant attack on Earth. John-117 begins on one of the three hundred space defense platforms that orbit the planet. After repelling the Covenant boarding parties, the battle shifts to Earth's surface. During the battle, a Covenant ship makes a Slipspace jump and the UNSC ship In Amber Clad, with the Master Chief aboard gets swept up in the ship's wake in a desperate effort to follow it.

The In Amber Clad is transported to the vicinity of another Halo ring - the Delta Halo - on which they land. Through an alternating game play story lines a power struggle within the Covenant is revealed, with Brutes usurping the role of the Elites. Furthermore, there is a movement, regarded by the Covenant leadership as heretical, which argues that Covenant teachings aren't true. Lastly, a Flood entity known only as the Gravemind, the controlling mind of the Flood, is discovered. The creature is obviously highly intelligent and gives the impression of knowing a great deal.

The Halos, as revealed by 343 Guilty Spark, were built to prevent the Flood from spreading throughout the galaxy, and that the Forerunners who built it were wiped out when they fired it as a "weapon of last resort" at some point in the remote past. In spite of this the Covenant activates the ring in preparation to fire, to bring about the Great Journey. Through gameplay the Index is retrieved and the Halo cannot fire. 343 Guilty Spark reveals that although the Index was removed before Delta Halo had time to complete it's firing sequence, it sent signals to other Halos in the Galaxy, putting them on standby mode. Now, they can be activated remotely from the Ark, whose exact location is not revealed at this point.



Battle of Onyx
In Halo:Ghosts of Onyx, which tells the story of the events that occurred on the planet Onyx, begins with a group of SPARTAN-IIIs deploying to a Covenant fleet refueling depot on Pegasi Delta. They proceed to destroy the facility, but due to unexpectedly heavy Covenant resistance, all but two of the three hundred Spartan team is wiped out. The only survivors, Tom-B292 and Lucy-B091, are revealed to be only twelve years old, and Lucy is traumatized and rendered mute.

The novel then cuts to a raid by the SPARTAN-II Blue Team on a rebel base at planet Victoria to recover stolen nuclear warheads. The team is nearly captured by a rebel ambush, but is saved by the timely, intuitive intervention of Kurt-051. Shortly afterward, the novel cuts to a meeting between the top leadership of ONI. In this meeting, they agree that the SPARTAN-II program is prohibitively expensive and that a more streamlined, "disposable" breed of Spartans must be trained for high-risk operations.

Trained on the restricted planet of Onyx the top three teams of the S-III Gamma Company, Teams Saber, Katana, and Gladius, conduct a training exercise run into some previously undiscovered Forerunner Sentinels. Through a series of events the Covenant are herd to the existence of Onyx and the human force discover an ancient Forerunner city, and are guided into a massive dome by Halsey, who determines that the entire planet is a construct referred to by the Forerunners as a Shield World. Fighting off determined Covenant pursuers, they press on into the heart of the planet to discover that the planet is literally a massive bomb shelter for the Forerunner to survive the activation of the Halos. Entering a slipspace rift in the planet's core, they find themselves alone in a vast Dyson sphere habitat. Kurt-051 stays behind to activate a pack of FENRIS warheads, thus killing himself, the Covenant pursuers. Onyx itself disintegrates, and is revealed to be an artificial construct composed of billions of Sentinels.



Battle of Earth
Halo 3: ODST tells the story of what happened after the Covenant slipspace jump that destroyed the port city of New Mombasa in Halo 2, as seen from the eyes of The Rookie, an ODST Orbital Drop Shock Trooper, and his squadmates.

Prior to the slipspace rupture in Halo 2, a large number of ODSTs are destined to drop into the Covenant carrier that evaded Earth's orbital defenses. The drop is initiated, but the ODST squad of Gunnery Sergeant Edward Buck is commandeered by his superior, and former love interest, Captain Veronica Dare of the Office of Naval Intelligence to drop into the city of New Mombasa, as opposed to the Covenant carrier. The slipspace rupture causes the assault on the carrier to fail, and the squad to scatter and land in different parts of the city.

The Rookie wakes about six hours later and must find his squad. He roams the night-time city, fighting off covenant patrols and discovering, with the aide of the city's Superintendent AI, clues that allow him to discover the fate of his fellow squad mates (with each discovery putting the player into that squad member's place for a level). He then picks up on Captain Dare's distress signal. The Rookie fights his way into and through an underground facility where they meet up, and continue to fight their way through a massive Drone hive (wakened by the earlier detonation of an ONI Building at the top of the shaft at the hands of Mickey and Dutch). They both fight their way to the Superintendent data core, and discover a Covenant engineer, one of many biological supercomputers and unwilling assistants to the Covenant, whom has taken apart the Superintendent's memory core and possesses vital information on the Covenant which could turn the tide of the war.

They, along with Buck, fight their way to the highway, and then down it, when they are forced to turn off the highway (wrecked in the beginning stages of an attempt to glass New Mombasa) where they hold off against waves of Covenant until Mickey, Dutch and Romeo arrive to pick them up. They arrive just before the Covenant prepare to glass their previous position, actually discovered to be an excavation project. They manage to escape just in time, only to realize that the Covenant has found what they were looking for.



Late Battle of Earth and Installation 00
Halo 3 takes place two weeks after the end of Halo 2. The Covenant have all but obliterated human resistance on Earth, and have committed most of their forces in East Africa, near the ruins of Mombasa. Marines and the Arbiter recover the Master Chief John-117 after jumping from the Forerunner Dreadnought as it entered Earth's atmosphere, and they all make their way back to the local UNSC base, Crow's Nest. The Master Chief defends the base, and is cut off, along with a small group of Marines. They make their way to the town of Voi along the Tsavo Highway through numerous Covenant outposts.

It is revealed that a large Forerunner artifact has been dug up under the African desert by the Covenant, and the Prophet of Truth is going to activate it. Presumably this is the Ark, so therefore this would activate the Halos, and so a hasty attack is set in motion by Lord Hood to destroy the Forerunner Dreadnought with a surprise aerial assault. Master Chief clears Voi of all Covenant anti-air units to clear the path for Lord Hood's frigates for an assault on the dreadnought. However, the assault on the dreadnought has absolutely no effect, and Truth activates the artifact all the same. A large portal is created above the artifact, into which the Covenant forces disappear. Soon after, a derelict Covenant cruiser appears out of Slipspace, and crashes nearby, infested with Flood.

The Master Chief and the Arbiter make their way toward the ship, and as they near its location, a group of Elite-controlled cruisers appear, striking up an alliance with the Humans and helping rid the city of Flood. Master Chief enters the ship and retrieves a message from Cortana, warning that High Charity is heading to Earth, full of Flood. It is decided that only the frigate Forward unto Dawn, the ship of Miranda Keyes, along with the Elites, will go through the portal after Truth, and stop him from activating the rings, as well as finding the 'solution' to the Flood that Cortana's message spoke of.

The Human/Elite force arrives at The Ark, and engage the Brute fleet. Master Chief makes landfall and finds the Cartographer of the Ark, which leads him to the location of the remaining Covenant Loyalist forces, at the Citadel. This leads to a trident strike at three shield generators guarding the Citadel at the heart of the Ark. Once all three generators have been deactivated, The Master Chief and the Arbiter breach the Citadel after Truth kills Miranda Keyes and forces Sergeant Major Avery Johnson to activate the rings. Upon executing the Prophet of Truth, the forged alliance between the UNSC-Separatist Forces is broken, as their cause to eliminate The Covenant is complete. After the Master Chief and the Arbiter escape the Flood, they discover that a new Halo is being built to replace Installation 04 which is nearly complete. The Master Chief decides that the only way to destroy the Flood was to activate the newly built Halo, which was out of range of the other installations, with Cortana. The Arbiter leaves to gather the surviving forces and get them ready to leave, and the Master Chief heads to the crashed High Charity to recover Cortana. After wading through tantamount to infinity of Flood, he recovers her and escapes to the new Halo with the Arbiter.

After fighting their way up to the top of the Control Room, the Master Chief and the Arbiter enter the Control Room, and attempt to activate the ring. However, 343 Guilty Spark attempts to stop The Chief and Johnson from activating the ring, saying that the charging sequence of the incomplete Halo will prove too much for the structure, and cause it to tear itself apart. In the fight, 343 Guilty Spark mortally injures Johnson, but fails at killing Master Chief, whom destroys him with a Spartan Laser. They succeed in activating the ring, however as expected, the installation begins to fall apart, and once more does Master Chief makes an attempt to escape Installation 04 in a Warthog. The two board the Dawn, which then proceeds toward the portal. The Dawn heads into the portal just as Halo fires, which closes as it gets halfway through shearing the Dawn in half.

Half of the Dawn, as well as the Arbiter, crashes back on Earth, and a memorial service is held for those who perished in the Covenant/Human war, ending on the note of the Master Chief's death.

At the end of the credits, a last cut scene shows that the Master Chief survived, and put himself into cryosleep, as Cortana activates a distress beacon. The rear half of the Forward Unto Dawn is seen hurtling through space toward what most fans believe to be a Forerunner planet.

In our universe
The first Halo title Halo: Combat Evolved quickly became known as the first "Killer App" for Microsoft's popular Xbox video game console when it was released in 2001, achieving both critical acclaim and financial success. Halo was later published on the PC and finally released for the Mac (for which it was originally developed prior to Microsoft's acquisition of developer Bungie). Shortly after that, the company (Gearbox Software) that ported Halo to PC released Halo: Custom Edition as a free, downloadable and achievable extension to the Windows port of Halo.

The second game, Halo 2 was released in 2004, breaking sales records and becoming the fastest selling United States media product in history. Halo 2 US sales top 125 million dollars; UK retail celebrates successful launch September 7.

A third game, Halo 3, has been released for the Xbox 360 and closes this chapter in the Halo series. The Halo games have become well known for the high quality of their graphics, gameplay, physics, and storyline. Halo Wars, a Real Time Strategy game, was released for the Xbox 360 in 2009. Halo 3: ODST, another First-Person Shooter, was also released in 2009. The newest game in the franchise, Halo: Reach, was released in 2010. Further expanding the Halo universe are several novels, which provide insight into the background story.