- "This isn't war, this is judgment!"
- —Unnamed Brute Chieftain
The Great War, also known as the Human-Covenant War, or the War of 10,000 Days, 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 lasting approximately 10,296 days (nearly 28 years). There were two additional factions sporadically involved in the conflict; them being the Flood, and a small number of surviving Forerunner constructs. Both 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 November 2552.
The war was ultimately made real by the Assembly, a network of illusive AI that met in secret to discuss the path humanity would take. At the end of the war it was revealed that the Assembly were really a network of extremely rampant Forerunner AI that had been left on Earth after their fall, and have in large part been responsible for every major military conflict in human history since the 2400's. The Assembly went so far as to sacrifice human colonies to the Covenant, which they claimed was to determine the Covenant's pattern of operation and design effective countermeasures. In 2552, upon the release of the Flood, the Assembly made themselves known to humankind, and quarantined all ships from leaving Earth.
Battle of Earth
The war concluded with the Battle of Earth, a conflict which lasted from October 20, 2552 until December 2, 2552 (although combat did not conclude until March 3, 2553), and was fought between the Last Combined Fleet of the Covenant, which arrived shortly after Truth fled Earth for the Ark, the remaining Flood forces, and the UNSC Home Fleet, eventually leading to the discovery of a network of structures beneath the portal to the Ark, and is in fact revealed to be a Forerunner structure used to contain and study the effects of a Flood Hive, and upon activation, unleashes an infestation the likes of which no species alive has ever seen. The battle intensifies upon the Assembly's revelation to humanity, and that they had begun a mass quarantine of Earth, claiming it to be in the best interests of Earth. Shortly thereafter, Blue Team regroups at the site of the Artifact, given orders by Hood to find the source of the Assembly and destroy it. Hood then activates Operation: REVELATION, as an attempt to locate the Flood's weakness, and disable it. It would be the final act in the Great War.
David-010, now commander of Blue Team, so strongly believes that the Assembly is attempting to enslave humanity and truly are Forerunner AI from past times, that he leaves Blue Team in an attempt to find the weakness of the Assembly, the machine elite, above all. David-010 goes on a solo-mission into the Flood infested depths of the Artifact, and is never to be seen again. The fighting continues on the surface, which escalates one more time when URF ships arrive. The fighting fluctuates throughout the battle between conflicts amongst UNSC and URF forces and a co-op between the URF and UNSC against the Covenant. Blue Team eventually locates and kills a which dis-coordinates the Flood Infestation, allowing the UNSC and URF to make a strong offensive against Flood controlled Africa and parts of the Middle-East, however, it is eventually discovered that they aren't making the dent they had hoped in the Flood forces. Right when they thought it could never happen and that the Flood had already won, the Covenant fleet arrived, and the human forces thought they were doomed. However, the Covenant ships opened fire on the Flood. The three factions were momentarily aligned in peace and tranquility against a common enemy. When the Flood forces had thinned, and most of the area of infestation had been glassed, the now allied UNSC, URF, and Covenant Empire took mainly to ground combat, and by March 3, 2553, most of the Flood had all been killed. At the end of the war, nobody heard from the again, nor did they LCDR David-010, or MCPO John-117. As far into the future as the 2600's nobody has heard from either of the enigmatic SPARTANS, and while John-117 was hailed as a hero, many people thought David-010 as being crazy, since his theory about the Assembly has never been proven right and is generally considered to be unrealistic in the eyes of the common human populace, but it has never been proven wrong either, and there are groups of conspiracy theorists who agree with his views.