Unified Earth Government
The Unified Earth Government, or UEG, is the central civilian government that administers Earth and its colonies
throughout a portion of the Orion Arm of the Milky Way galaxy. It houses the Colonial Administration Authority, the UNSC, as well as the UN.
The Unified Earth Government traced its origins back to the Interplanetary War of the mid- to late-22nd Century in the Sol system. With numerous Earth governments fighting independent battles against Frieden and Koslovics forces, the UN became involved, eventually using the war to absorb most, if not all Earth governments into itself, forming a global government to combat the terrorists and stabilize the planet and its other world colonies.
The UN won the war and the Unified Earth Government was formed, with its' primary defense, scientific and exploratory force being the newly formed UNSC.
Although the UEG seemed to have complete control over Earth and its colonies, the UN still existed as an organization and a political entity in the 26th century.
During the Human-Covenant war, the UNSC assumed the governing function of the Unified Earth Government in the face of the overwhelming Covenant threat.
Following the end of the war and the inauguration of Dr. Ruth Charet the UNSC handed back civilian powers on January 8, 2553.
Covenant Empire
The Covenant Empire, also referred to as The Covenant, was a theocratic hegemony made up of multiple alien species that maintained control over a large portion of the Orion Arm in the Milky Way galaxy.
The Covenant was a political, military, and religious affiliation, originally a mutual alliance between the San 'Shyuum and Sangheili following a brutal conflict between the two warring races.
Its expansion to include at least six other races united in the worship of the Forerunners and the Halo Array soon began after the original formation.
The Covenant waged a genocidal campaign against humanity, until they were formally defeated due to many factors - the most crucial of which was an internal conflict.
Whilst the Covenant's main leadership was either lost during the Flood infestation of High Charity or during the Battle of Installation 00, the Covenant continues to exist even after the conclusion of the war.
A splinter faction of Sangheili loyalists remains known as the Covenant Remnant; this terrorist group is deemed hostile to Humanity, breaking the truce formed at the end of the initial war with the Covenant.
They have been seen to field large numbers of warships, but their true power, and indeed the number of Covenant involved with their activities, is unknown.
It is also unknown in what capacity the other parts of the Covenant continue to exist, or even if any other fragments of this once-great empire remain.
Covenant Remnant
The Covenant Remnant, founded and led by Supreme Commander Jul 'Mdama, emerged in the wake of the Human-Covenant war, the Great Schism and the disappearance of the San 'Shyuum.
Like the Swords of Sanghelios and Merg Vol's faction, 'Mdama's faction considers itself to be a legitimate successor to the original Covenant Empire, and thus the faction is known by its followers simply as the Covenant.
Although the faction is generally recognized as a continuation of the original Covenant, its members are identified as terrorists by the UNSC and the organization itself is regarded as closer to a religious cult as opposed to a full-fledged empire like the original Covenant.
Swords Of Sanhelios
The Swords of Sanghelios are a break-away faction of the Covenant composed predominantly of Sangheili.
The movement was originally founded as a rebellion against the San 'Shyuum-led Covenant after the Sangheili learned of the true nature Halo Installations near the end of the Battle of Installation 05 in November 2552.
Following the end of the Human-Covenant war, the Swords of Sanghelios rapidly grew in scope and influence, eventually taking control of Sanghelios and the majority of the Sangheili inner colonies.
The Swords of Sanghelios are also one of a very select few breakaway Covenant factions to maintain diplomatic relations with humanity following the end of the war.
By March 2553 Thel 'Vadam had become the de facto leader of the Swords of Sanghelios and was still in power as of 2559.
While the Swords of Sanghelios maintained a solid following, they met resistance from numerous conservative factions which held true to the Covenant religion or to the religion of ancient Sangheili.
Ecumene/Forerunner
The Ecumene is the formal name of the galaxy-spanning Forerunner empire which existed over 100 thousand years ago and consisted of three million or more planets.
The political center of this empire was known as Maethrillian, a massive structure containing multiple cities.
The Forerunner race were a highly advanced and ancient species whose empire,
the Ecumene, was spread across three million fertile worlds in the Milky Way galaxy approximately 100,000 years ago.
The Forerunners were the creators and builders of many significant installations, including the Halo Array, the Ark, and the Shield Worlds, as well as numerous lesser artifacts later found on many worlds.
The Forerunners had taken up a role as custodians of the galaxy and believed that the "Mantle of Responsibility," the center of their society and culture, had been passed down to them by the Precursors, an even more powerful race that preceded the Forerunner civilization.
"Forerunner" is a literal translation of the species' name for themselves; they identified themselves as such because they believed that they held an impermanent place in the universe's Living Time and that they would be succeeded by other, better races.
Before their disappearance from the galaxy, the Forerunners would name humanity their successors, identifying them with the title "Reclaimer".
The alien alliance known as the Covenant worshipped the Forerunners as gods, deriving much of their technology from Forerunner artifacts found throughout the galaxy, and believing any who defaced these relics to be Heretics.
Prometheans
The Prometheans were the highest and most respected group of Warrior-Servants in the Forerunner Ecumene.
During and after the Human-Forerunner war, they were led by the Ur-Didact. The Prometheans' main base of operations was the Shield World known as Requiem.
During the Forerunner-Flood war, the Prometheans were converted into digital intelligences, known as Knights, by the Forerunner machine known as the Composer.
These constructs, along with the Didact, survived the activation of the Halo Array, eventually awakening within Requiem and becoming a new threat to the UNSC in 2557.
The Flood
The Flood or the Parasite, as they are known to the Covenant, are a species of highly virulent parasitic organisms that can reproduce and grow by consuming sentient life forms of sufficient biomass and cognitive capability. The Flood was responsible for consuming most of the sentient life in the galaxy, notably the Forerunners, during the 300-year-long Forerunner-Flood war. The Flood presents the most variable faction in the trilogy, as it can infect and mutate Humans and Covenant species, such as Sangheili, and Jiralhanae, into Combat Forms. They are widely considered to be the greatest threat to the whole existence of life, or, more accurately, biodiversity, in the Milky Way galaxy.