Flood. A civil war between the Forerunner's dictator known as the Didact, who wanted to assimilate all the humans on Earth into his army as AI's, thus immune to the flood, and his wife the Librarian, who created the Ark, an instrument which allowed for the mass creation of Halo installations which could all be activated simultaneously. The Librarian, along with all the remaining forerunners, trapped her husband inside a Forerunner repository of knowledge known as the Domain, activated the Ark and disappeared. Nearly a hundred thousand years later in the 26th century, humanity—under the auspices of the United Nations Space Command, or UNSC—colonized many worlds thanks to the development of faster-than-light "slipstream space" (i.e. hyperspace) travel. Tensions between the government and colonies desiring independence sparked violent clashes. The UNSC sponsored the SPARTAN-II Project to create an elite group of enhanced supersoldiers to suppress the rebellions covertly. In the year 2525, human worlds come under attack by an theocratic alliance of alien races known as the Covenant, whose leadership declared humanity heretics and an affront to their gods—the Forerunners. The Covenant began a genocidal holy war. Their superior technology and numbers proved decisive advantages; though effective, the Spartans were too few in number to turn the tide of battle in humanity's favor. After the Covenant invaded Reach, the UNSC's last major stronghold besides Earth, Master Chief John-117 was left as one of the few remaining Spartans. The rediscovery of the Halo rings set the humans against the Covenant, who believed they were instruments of transcendence, not destruction. Master Chief and his artificial intelligence Cortana were instrumental in the destruction of a Halo ring to stop the Covenant and the threat of the Flood. Master Chief defeats the Prophet of Regret leading to the Prophets of Truth and Mercy denouncing the Sangheili as the most honourable species amongst the Covenant. This begins a civil war within the covenant, with many grappling over the revelation that their religion was false. The disgraced former Covenant Sangheili commander known as the Arbiter, along with the rest of his race, helped the humans destroy the Covenant and stop the Prophet of Truth from activating the Halo Array via the Ark. The Human-Covenant War ended, though new conflicts begin to emerge throughout the universe. In the post-war era, the UNSC creates a new generation of Spartans, and tensions between the UNSC and colonist rebels resumed. The