The origins of humanity lay in the ancient race of beings known as the Precursors. Responsible for seeding the galaxy with life, the Precursors genetically engineered early humanity millions of years ago along with many other species in the galaxy, including Forerunners, a would-be rival species to humanity. The Precursors achieved this by creating the two species from the same base stock, splitting a species they created apart so that they would evolve separately. The Precursors intended humanity to inherit the Mantle, their assumed role of guardianship for all life in the galaxy and for countless generations prepared them for this role. The Forerunners refused to accept this decision and subsequently rebelled against the Precursors. After exterminating the Precursors to the point of extinction, the Forerunners claimed the Mantle for themselves, using it not only as the basis of their society but also as justification for securing their own dominance for millions of years.
Humanity achieved an advanced state early in its history, well over 1,100,000 BCE, when their earliest, long-forgotten cultures attained space travel and spread across many worlds. The latest of these early civilizations, having risen to power around 150,000 BCE after a series of technological dark ages, eventually reached a level of technological sophistication close to that of the Forerunners. Humans of this era were on average larger and superior to modern humans in many respects, including intelligence and physical strength.
Humanity resented Forerunner dominion over the galaxy, and as a result expanded their civilization outward along the Orion Arm and across the galactic margin, away from the Forerunners' sphere of influence. This civilization formed an alliance with the San'Shyuum and later warred against the nascent Flood. While humanity lost a third of their population, the Flood was eventually driven out of the galaxy. However, the conflict led to a war with the Forerunners, a war which humanity lost. As punishment, the humans were stripped of their technology, nearly all evidence of their civilization was erased from the galaxy, and the scattered remnants of their species were exiled to their homeworld, genetically "devolved" to more primitive forms and reduced to a pre-technological state from which they would be forced to start again.
Following the firing of the Halo Array, the surviving humans were returned to Earth, being the first species the Forerunners reintroduced. These reintroduced humans would witness Forerunner sentinels burying the Excession, with one of them leaving an Out-of-place handprint nearby. Societies began developing from then on. One of the earliest known societies founded was around the 5th Millennium BCE, when Egypt was formed.
In this early recovery, these societies began fighting each other; the histories and tales of which would be passed down hundreds if not thousands of years. Examples include 300 soldiers from Sparta defended Greece at Thermopylae in 480 BCE and Marcus Agrippa saving Rome at the Battle of Actium.
The United Nations first established the Unified Earth Government in 2075. Luna, Mars, the Jovian Moons and several asteroids would first be settled by humans in the First Diaspora, beginning in 2080. 2090 and 2103 also saw the ends of large scale conflicts. In the 2100s, the British Houses of Parliament were destroyed in a domestic terrorist act. Gene therapy by the 2100s also functionally wiped out cancer.
he Interplanetary War in the 2160s marked a major shift in humanity's governance: after a violent conflict spanning the Solar System, the UEG was formed into a true governing body in charge of all human nations. While growing overpopulation on Earth continued to pose challenges for the new government, the development of Slipspace travel in 2291 helped the UNSC engage in spreading the human race beyond their home solar system, relieving the serious ecological pressure on the home world.[5]
This expansion was to usher in promising new opportunities for humanity, as some of these colonies, such as planet Reach with its bountiful titanium deposits, could offer abundant stores of raw materials that may had otherwise been considerably unique and scarce on Earth. With the initial advent of interplanetary trade driving down the costs of what may had once been an expensive implementation of their technology - such as the forging of space-worthy ships and naval vessels - the effects from these carefully implemented first colonization projects helped to ensure that interstellar trade, travel and communication were to be more commonplace amongst the general populace in the ensuring centuries, eventually granting humanity the capacity to establish colonies at enhanced rates. In the background, the progress of human civilization was being subtly manipulated for hundreds of years by the The Assembly, a shadowy collective of AIs committed to humanity's survival.
After over a century of prosperous expansion, humanity's populations had spread relatively thin across hundreds of worlds in a volume of space dozens of light-years across. The colonies had become divided among the Inner and Outer Colonies, the former representing the first established, stable and wealthy populations and while the latter were responsible for supplying a large portion of the resources that allowed the core worlds their high standard of living. As predicted by sociologist Dr. Elias Carver, a buildup of discontent among the Outer Colonial populations eventually culminated in the onset of numerous brushfire wars across the Outer Colonies which would come to be known collectively as the Insurrection. The UEG's fear of these civil conflicts escalating into a projected apocalyptic war between the Inner and Outer colonies led to the creation of the ORION and SPARTAN-II super soldier programs, along with extensive UNSC military campaigns across the colonies. These pioneering efforts would pave way for safer and more widespread human augmentation, with Spartan super soldiers being produced in increasingly large numbers over the following decades.
After decades of internecine conflict, humanity as a whole was forced into their first major war against an outside opponent when they were discovered by the genocidal alien hegemony known as the Covenant. As the decades-long war wore on, the human species gained the reputation as a worthy adversary against the Covenant, despite the fact that they were technologically and numerically inferior. Despite the fact that humans could hold out and even defeat the Covenant on ground combat, the Covenant could in turn withdraw to space where they had virtually undisputed supremacy and would be capable of glassing the planet.
Humans have been able to show great bravery when facing insurmountable odds. Some of the members of the Covenant wondered why their leadership had refused to allow the humans to join them, as they had been able to hold steadfast even when outmatched in almost every way. However, despite great courage and tenacity, the future seemed dark for the survival of the human race as the Covenant continued to methodically exterminate their colonies, marching ever closer to Earth, eventually discovering and invading it on October 20, 2552. In the ensuing battles over possession of Earth, humanity suffered heavy casualties.
Following the final battle of the war on December 11, 2552, the Human-Covenant War ended in a victory for humanity and their newfound Sangheili allies - the majority of the Covenant military having been defeated at Delta Halo by the Sangheili Fleet of Retribution, while the rest were annihilated by the joint Elite-UNSC forces at the Ark. This victory came in time to save the human home world, thanks chiefly to the actions of Arbiter Thel 'Vadam and Spartan John-117. The Human-Covenant War was officially declared over on March 3, 2553, when a memorial service was held near Voi, Kenya, to those fallen during the 27 years of fighting.