Human-Promethean war

The Human-Promethean War is an ongoing conflict that began approximately on July 20th, 2557 on the Forerunner shield world called "Requiem." The Covenant remnant, led by Shipmaster Jul 'Mdama, first engaged UNSC forces during the boarding of the derelict wreckage of the. UNSC reinforcements would subsequently arrive to fight a Covenant effort now aligned with the Didact and his legions of mechanized Prometheans.

Background
In ancient times, the human race was a great interstellar empire. During the course of their growth as a civilization, they encountered a terrifying threat: an extra-galactic parasite known as the Flood. As the parasite ravaged their worlds and threatened to consume their entire species, humanity fled outwards from their home territory. As they did so, they attacked any Forerunner world where an infection had taken hold, neglecting to warn the Forerunners of the threat in favor of bombarding infected areas immediately. Ignoring their warnings about the dangers posed by the Flood, the Forerunners - led by the Didact and his Promethean Warrior-Servants - defeated humanity and forcibly devolved their civilization. However, the Forerunners were left vulnerable by the long conflict: their military had been weakened, and all information regarding the mysterious threat that humanity had been fleeing was lost. After a period of calm, the Flood returned, and the Forerunners were ill-prepared to fight back.

The Forerunner Builder rate had prepared for this eventuality, creating a number of ring-shaped superweapons known as Halos. However, the Didact was reluctant to use these, and instead planned to use the Composer, a device capable of transferring organic consciousness to software, as a means to save the galaxy's populace from Flood infection. But the process was flawed, and those who underwent the process were corrupted, driven insane and unable to be re-uploaded to an organic form. This, however, suited the Didact's purposes: he would use the Composer to convert his Prometheans into mechanical warriors, later augmenting their numbers with converted humans to create a massive army to fight the Flood. In his view, this was both an elegant solution to the Flood problem and a means of neutralizing the human threat forever. However, his wife the Librarian was horrified by his actions, and sealed him inside the shield world Requiem, which was his base of operations. The converted Prometheans were left there to guard his Cryptum, and Requiem remained quiet for millennia after the Forerunners were wiped out by the Halo Array.

In the year 2554, the planet was found again. Seeking both a new spiritual voice for their people and a chance for revenge against the victorious UNSC, a remnant faction of the Covenant sought to unlock the world's secrets. Additionally, their shipmaster, Jul 'Mdama, had learned the Didact was trapped inside and sought to release him in order to achieve vengeance on humanity. In orbit above the planet, however, was the wreckage of the UNSC Forward Unto Dawn. In the first skirmish of the war, Covenant warriors attacked the vessel in hopes of deterring the humans' efforts.

Entering Requiem
The reawakened John and Cortana defeated the advanced scouting teams and reactivated the Dawn's weapon systems manually, destroying a CCS-class cruiser in the process.

After scanning the vessel and detecting a Reclaimer, Requiem's automated systems pulled both the Dawn and the Covenant force surrounding it through the world's outer shell and down to the planet's surface. Recovering a Warthog, Master Chief and Cortana vowed to make their way back to Earth in order to find a cure for Cortan's escalating Rampancy. They set out to find a way to contact the UNSC, circumventing the powerful jamming field surrounding the world.

Fighting through numerous Covenant hunting parties, Master Chief was attacked by advanced Forerunner defense drones which Cortana identified as Prometheans. Evading or destroying pursuit, John attempted to warn the approaching UNSC Infinity of the dangerous energy field that had disabled the Forward Unto Dawn.

After disabling two control nodes, it became clear that a great threat had been imprisoned within Requiem. The Didact, the Forerunner's greatest warrior and the individual responsible for firing the Halo array 100,000 years ago, remained in suspended animation within a Cryptum. Easily disabling John with his powerful abilities, he declared the return of the Forerunners as the galaxy's rulers and saviors. Humanity remained weak and unworthy in his eyes of inheriting the Mantle, a view rejected by his lover, the Librarian. Having always revered the Forerunners as gods, the Storm quickly swore alliance to the Didact and his armies. The Diact viewed the Covenant as mere primitives, but permitted them to serve his cause, to prevent the ascension of the human race to galactic prominence.

Narrowly escaping the collapsing command center, the Chief and Cortana returned to the planet's surface only to find their warning to the Infinity came too late. The massive warship crashed more than 70 kilometers away, with a massive force of Covenant and Prometheans closing on their position.

Evading capture, John was successful in regrouping with a group of SPARTAN-IVs led by Commander Thomas Lasky. Recognizing the Chief immediately, Lasky asked John and Cortana to clear a landing zone so that Infinity's ground forces could fall back to the ship which had fallen under siege. Commandeering a Scorpion tank, John led the attack to the crippled vessel alongside Commander Sarah Palmer's Spartans. Using the UNSC's latest weapon, the Mantis exoskeleton, John rallied a force of nearby Marines and regained control of the ship's interior. After reinitializing the ship's secondary MAC guns and missile batteries, the tide turned in the UNSC's favor. Two CCS-class cruisers and dozens of dropships were destroyed in the artillery barrage, while the Didact's Cryptum was forced to retreat.

With a momentary lull in the fighting, John was called to a strategy meeting with Andrew Del Rio, Captain of the Infinity. Skeptical of the threat of the Prometheans, Rio ordered an immediate attack on a Forerunner gravity well preventing the ship from leaving. A strike force of Spartans led by John was deployed with a Mammoth-class ultra heavy ground vehicle supporting the attack. Facing daunting odds, the UNSC was able to defeat a large armored strike force of Covenant and Promethean and disabled the gravity beam. Upon reaching his objective, John was confronted with a vision from the Librarian, who warned him of the Didact's true plans. After explaining their history to them, she provided John with a gift, a medical treatment to counteract the Forerunner's devolution of the human genome, and a means to resist the Didact's plan to enslave the human race once again.

Regrouping aboard the Infinity, Captain Del Rio dismissed the threat of the Prometheans and prepared the ship to depart the system. Defying direct orders, John took the increasingly unstable Cortana and departed the Infinity. Armed with a Pelican gunship provided by Commander Lasky, John launched several attacks on support pillars providing the Didact's Cryptum with shield and power, with the goal of preventing him from leaving the planet and attacking Earth and other colonies.

The Composer
This attempt ultimately proved unsucessful, as the Didact left Requiem aboard his flagship, the Mantle's Approach, escorted by a flotilla of Covenant ships. Stowing away aboard a Lich, the Chief followed the Forerunner to Ivanoff Station, a UNSC research base orbiting Installation 03, the Composer's resting place. Sandra Tillson, a lead researcher aboard the base, helped guide John to the artifact amidst a swarm of Covenant attackers. Despite the Spartan reaching the artifact first, the Didact was successful in obtaining the Composer, tearing it out of the station's hull with a gravity beam. Testing the weapon, the Composer burned the crew of the station to ash, assimilating their forms to create even more Prometheans. The Master Chief's genetic enhancements rendered him immune to the device's effects.

Battle of Earth
With the Composer in the Didact's possession, the Forerunner was poised to deal a deathblow to Earth, and by extension humanity. Racing across the Mantle's hull aboard an F-41 Broadsword fighter, the Master Chief was surprised to find the Infinity and the rest of the Home Fleet ready and waiting for the Didact. John was able to destroy the ship's point defense guns, giving Infinity the chance to punch through the vessel's hull. Entering the breach, John fought his way to the Forerunner's location.

Despite the UNSC's best efforts, the Didact began to fire on Earth with the Composer, annihilating the population of New Phoenix, Arizona. Armed with a HAVOK warhead, John confronted the Didact for the second time. While John was unable to hurt the Forerunner with conventional attacks, the dying Cortana disabled the Didact's armor and immobilized him with hard light shackles. With the last of his strength, John used a pulse grenade to destroy the Forerunner's armor, sending him down into the Composer's energy stream. With time having already ran out, the Spartan detonated the nuclear bomb manually as a desparate last resort.

Using the last of her power, Cortana was able to create a hard light barrier to shield John from the blast, saving his life at the cost of her own. Left adrift in space, he was later recovered by the UNSC. Back on Earth, John rejoined Palmer and the SPARTAN-IVs, preparing for the inevitable battles ahead.

Return to Requiem
While their defeat at Earth proved a set back for the Promethean/Covenant alliance, it did not result in their defeat. Six months later, the Infinity battlegroup returned to Requiem with a fresh compliment of Spartans, determined to conquer the planet at any cost. The Covenant ships in orbit around the planet were swiftly defeated and scattered, demonstrating the technological advancement of the UNSC since the end of the last war. Arriving on the planet's surface, Majestic and other SPARTAN-IV squads began to disrupt Covenant operations across Requiem and recover Forerunner artifacts for study.

List of appearances

 * The Commissioning
 * Halo 4