The Halo Universe 101
Sweeping across the expanse of time and over the breadth of a thousand star systems, the tale of Halo is ultimately one of the human condition. It is a story about the frailty of mankind and their fight for survival against an implacable and unstoppable enemy known as the Covenant. And at the center of it all is the legendary Master Chief, the only thing that stands between humanity and extinction.
Long before humanity shed its own terrestrial bonds, an ancient race known as the Forerunners had already mastered the heavens. Using their advanced technology they took it upon themselves to protect all life in the galaxy. But when a threat emerged from the blackness beyond our stars, the Forerunners were caught off guard.
The Flood, a parasitic species that propagates by infecting sentient beings, had already infested a variety of worlds within the Milky Way. By the time the Forerunners took action, it was too late; the Flood had already surpassed any efforts at containment.
Fearing all would be lost, a group of Forerunners developed a plan to stop the parasite once and for all. They called this plan Halo. Using a massive installation known as the Ark, they built seven ring worlds, which they spread throughout the galaxy. This Halo Array, as they called it, when fired, would destroy all sentient beings within range, essentially starving the Flood to death.
Then, after staying the hand of judgment as long as they could, the Forerunners finally fired the rings and seemingly vanished from existence. The knowledge of the Halo Array and the Ark was lost for a time. All that remained was the hope that someone, somewhere in the distant future, would discover the truth.
One hundred thousand years later, humankind finally turned to the stars. But even after developing the technology of Slipspace travel, which allowed them to colonize distant worlds, they failed to learn from their own primitive nature.
Not long after humans built other worlds to dwell on, they began to war with each other. A powerful governing body known as the United Nations Space Command (UNSC) attempted to quell insurrectionist factions, but there seemed to be nothing that could halt the mounting tide of violence.
It was then that an agency known as the Office of Naval Intelligence (ONI) commissioned the SPARTAN-II project. This extreme measure sanctioned the abduction of young children who would be genetically engineered into the most advanced supersoldiers humanity had ever seen. And for a time, this solution worked flawlessly, the Spartans meted out swift judgment against any who resisted the UNSC.
But in 2525 CE, all of that changed.
Without warning, the Outer Colony of Harvest was obliterated by an unknown force, a force that would later reveal itself as the Covenant. This alliance of alien species believed humanity was a stain that needed to be wiped from the galaxy, and they committed themselves to this belief without any mercy.
Extinguishing every human population they could find, the Covenant were consumed with humankind's annihilation. However, despite being greatly outnumbered, the Spartans engaged the alien enemy in groundside conflicts, frustrating the Covenant’s advancement every step of the way. Ultimately, each terrestrial victory proved insignificant, since the Covenant dominated space battles without contest.
Still, it wasn't until they attacked the planet of Reach, Earth's veritable doorstep on the brink of humanity’s extinction, that these legendary Spartans fell.
Fleeing into Slipspace at a seemingly random vector, a UNSC warship brought with it what was believed to be the last remaining Spartan, the Master Chief. As they arrived in a remote, uncharted region of the galaxy, they suddenly came face to face with something they had never before seen Halo.
This prodigious discovery was marred when the Covenant, attempting to activate the ring to fulfill their specious prophecies, mistakenly released a strain of the Flood that had been contained within the installation for a hundred thousand years.
In response, the Master Chief was forced to uncover the secrets of the Forerunners' extinction and a stratagem to prevent the parasite from escaping. With the fate of the galaxy hanging in the balance, he destroyed Halo, ending the vast threat it possessed and destroying the Flood's infestation along with it.
The Ark and Aftermath
Ignorant to the truth of the Halo Array, the Covenant continued their quest and soon located yet another ring. When they failed to fire it, a chain reaction of events occurred that opened a portal on the planet Earth. This portal would lead any who entered to the Forerunners' most precious installation, the Ark, the only place where the Halo rings could now be fired.
It was here that humanity formed an unlikely alliance with a faction of Covenant defectors known as Elites, and together they assaulted the Ark. With the last vestige of Covenant forces attempting to activate the Halo Array, the Master Chief raced to the surface of a remote ring world, igniting its fire and obliterating both his adversaries and the Ark in the process.
For the survivors on Earth, the Master Chief is believed to have been killed, sacrificed to prevent humanity’s extinction. Little do they know, the Spartan miraculously survived and is now stranded in an unknown region of space without any way home.