“Ten thousand years ago, humans had fought a war against Forerunners—and lost. The centers of human civilization had been dismantled and the humans themselves devolved and shattered into many forms, some said as punishment—but more likely because they were a naturally violent species.”
Although Humanity was a far younger race than the Forerunners, they had always held Forerunner interference with contempt. Looking to escape from Forerunner control, Humanity expanded throughout the Orion arm, and eventually began building an impressive empire consisting of an unknown number of worlds. Before the war, Humanity had made great advances in military, science, and technology, rivaling those of the Forerunners. In his conversations with Bornstellar on their arrival at Charum Hakkor, the center of the human empire, the Ur-Didact stated that the Forerunners had little defense against the weapons created by the humans and San'Shyuum. By collecting and reverse-engineering Precursor technology at Charum Hakkor, one of the largest collections in the galaxy, Humanity's rapid technological achievements made willing challenges towards Forerunner policies. This, coupled with their belief that they - not the Forerunners - were the (true) inheritors of the Mantle from the Precursors, made them ideological enemies, and heretics from a Forerunner perspective. Essentially purists, Humanity during the Human-Forerunner wars moved indigenous species during their war. When Humanity annihilated 50 defenseless systems in which Forerunners had resettled other species during the war, that was the last straw. After displacing the indigenous populations of those systems, Humanity replaced them with human colonies to strengthen their hold over these new territories. Although initially successful in destroying and conquering many of those alien worlds, Humanity was eventually pushed back to Charum Hakkor.
Before the war, Humanity had reached Tier 1 technology on the Technological Achievement Tiers scale similar to those of the Forerunners. When Bornstellar obtained the Didact's memories, he gained insights into Charum Hakkor at the height of its powers. He described the implacable Precursor ruins of Charum Hakkor studded with Human constructs, like ivy growing on great trees: vast cities, energy towers and defense platforms operating at geosynchronous orbit and equigravitation, only a little less sophisticated than Forerunner ships, platforms and stations. Finally, he concludes that humans had been a great power, a worthy adversary—technologically.
Battle of Charum Hakkor and Humanity's collapseEdit
Although Humanity was successful in its early conquest of the alien worlds which the forerunners resetteled species on, they were forced to deploy the majority of their military against the Flood. By the time the Flood had been defeated, the Human military had been exhausted. Even the capital of Charum Hakkor had been cut off from the rest of the empire by Didact's naval fleets. On Charum Hakkor, Humanity had incorporated precursor technology and constructed formidable fortifications capable of standing out against even the strongest fleets. Among them were unbending filaments that link their orbital platforms defenses similar in concepts to the Orbital Defense Platform on Earth and Reach.
Despite having the combined Forerunner military at his disposal, it took the Didact great efforts to defeat the Human resistance and capture the capital. Among the casualties were all of the Didact's children. Although cut-off and unable to receive reinforcements from the San'Shyuum, the Humans held off continuous attacks for fifty years. When the planet finally fell significant numbers of Humans and San'Shyuum committed suicide rather than being taken prisoner. Although Humanity was completely and utterly defeated, the tragedies of the war convinced the Didact to oppose and forestall the construction of the Halo Array seeing it would violate the Mantle as the destruction of Humanity proved similarly, a task that he succeeded for thousands of years.
The defeat was disastrous for both Humanity and the San'Shyuum. The victorious Forerunners decided to dismantle almost every piece of pre-historic human civilization. In addition, they executed many Humans for starting the conflict, viewing them as naturally violent and aggressive. Because of this cataclysmic event, the race was splintered into many subraces, such as the Florians. This was noted as being a "punishment" by the young Forerunner pre-BuilderManipular, Bornstellar Makes Eternal Lasting, ten thousand years later.
Humanity's defeat affirmed Forerunner hegemony over the entire galaxy, as one of the only few powers capable of competing against them was utterly defeated. However, the destruction of Humanity set the stage for the return of the Flood and the disastrous Forerunner-Flood War, as the Forerunners proved totally inadequate in containing the renewed threat. The Didact later regretted the complete destruction of Humanity, since, earlier, he was unaware the Flood was the reason for Humanity's aggression during the Human-Flood War.
The San'Shyuum homeworld was placed under quarantine, with a Forerunner military fortress orbiting the planet. When The Librarian attempted to index the San'Shyuum during the early stages of the Forerunner-Flood War, the San'Shyuum mistook her intentions and rose in revolt against the Forerunners. The Master Builder took this opportunity to test Halo's effects on living beings, on the San'Shyuum homeworld; it surpassed all expectations. This genocidal act led to the near extinction of the San'Shyuum species, and Faber's removal from power and subsequent trial on charges of treason-against-the-Mantle.
↑With prehistoric human civilization completely dissolved from the galaxy, the species went into a devolved state recognized by historians since the evolution of modern science in the 19th, 20th, and 21st centuries.