The Interspecies Union is an organization formed not long after the end of the Human-Covenant War in order to keep the peace among the various species of the galaxy. It was founded by the humans and the Sangheili, and was joined by the Huragok and the Evaniptii in later years. The Union is simply a placeholder system to keep the alliance alive whilst the Covenant remnants are still active.
There is an annual congressional session lasting one human month (30 days) in which representatives of all the member species meet to rectify conflicting issues and propose new amendments in which to aid the Union. Thirty members from each represented species are chosen by that species' own jurisdiction. Each one serves a five-year term. If need be, an emergency session can be called by at least two species' Heads-of-State or by a 55% vote in session.
When the Human-Covenant War ended on March 3, 2553, both humanity and the Covenant Loyalists were left in a desolate state. The human population had been reduced from 40.7 billion to a mere 19.4 billion, only 200 million of them being military survivors. They were left with a mere nine colonies, most of which were scattered in distant systems too far away to properly support. The Navy had become reduced to sixteen capital ships, incapable of creating more than a half-hearted planetary defense against any major enemy threat. The Unified Earth Government had become disorganized and threatened to topple, which would in turn push human society into self-destruction. Foreseeing this possible danger, the United Nations Space Command struggled to maintain what strength it had left and reinforced humanity against potentially opportunistic rebels emerging from hiding to attack the weakened heart of Earth's government.
Chairman Locke's signature on the Interspecies Union Charter of Formation.
The Sangheili were not as physically weakened as a species, but their ideological strength had always been dependent upon that of the Covenant's, and it completely collapsed when word of the Great Schism reached Sanghelios. When the Fleet of Retribution had returned home, they faced a situation that was different but equally as dangerous as humanity's; the keeping of peace among their clans and families. Although their population remained steady, the predicament on Sanghelios had become chaotic. A great number of Sangheili culture had been integrated with that of the Covenant's for the past few centuries, and the sudden revelation that the Great Journey had been a lie created massive feuds between the families. As if adding insult to injury, the Separatists' alliance with humanity had caused an uproar, and was widely considered an act of dishonor. The Sangheili began to break into separate factions, some taking the side of the Separatists, some demanding to break away from the humans, and even some still believing in the Great Journey. Despite ArbiterThel 'Vadam's efforts to unite the Sangheili, several antagonistic factions were quickly formed, the most notable at the time being The Fallen.
With both species realizing the toll that the war had taken on them, the Unified Earth Government quickly established contact with the Separatists and offered to form an alliance, to settle the disputes that had arisen internally in both societies and to strengthen the other against enemy factions such as the Covenant remnants. The fragile peace held for several years, enough for the UNSC to create the Reformation Act of 2555, and tentatively created the Interspecies Union with the Sangheili. The official treaty was put into effect on October 1, 2556.
After the Human-Covenant War, the Sangheili had provided humanity with tier-2 technology to help bolster their rebuilding. While it was reliable and useful, their lack of original understanding had made it hard for humanity to fully utilize. Even the Sangheili knew little more than how to use it, and without the Huragok to help them, the initial progress on adaptation was slow. However, humanity did its best and in return helped the Sangheili improve their efficiency on tier-2 resource usage. After the Interspecies Union obtained an abundance of tier-1 technology in 2556, some of which included basic Forerunner-class AIs, the developments began to pick up. However, it wasn't until the Huragok joined the Union in 2570 that they really began to progress technologically at a rapid pace.
The Interspecies Union had also made abundant discoveries of Precursor assets as their understanding of Forerunners expanded, however their understanding of tier-0 technology has remained basic.
"We're taking a big risk here, gentlemen. I am aware of that. But survival is the highest priority on our agenda right now, and the creation of these Spartans might be the only thing that stops the Covenant, wherever they're lurking right now, from coming back to Earth and slitting our throats. It's not an easy decision to put so many resources into the program, and it might come back to bite us in the ass in a few years. But to hell with it, my focus is to keep everything together for now, and I intend to act accordingly."
With humanity's change in direction after the Reformation Act of 2555 was passed,
the SPARTAN-III Program was instantly reestablished. Although the Act ensured that costs had been reduced to an absolute zero, the UNSC was scraping every last bit of resources into making sure the 3000 trainees of Delta Company would be enough to sustain the military for the next few decades. During this time, the usage of resources was kept to a minimal, and humanity relied heavily upon importing additional resources from Sangheili, an action that was hesitantly put into compliance. Still, the Unified Earth Government was constantly short on resources at this point, and time began to run out as the drawbacks in Locke's short-term plan would soon have severe repercussions unless dealt with.
However, the long-term issue was solved in 2556 when the Interspecies Union had a brief encounter with Forerunner survivors that had been found on April 24 at the remains of a destroyed Eridanus II. The Forerunners themselves, however, had been divided, some siding with the Union and some against it; when the Union had won on August 7, the remaining allied Forerunners had departed but left them with many tier-1 technologies that moved both humans and Sangheili forward by centuries when they adapted the technology. Although this had not made the Union nearly as advanced as the Forerunners had once been, it did speed up the rebuilding process of colonizing planets, as well as holding enemy factions at bay more easily and filling up humanity's nearly depleted resources. It also extended the potential usefulness of Delta Company from decades to centuries, and even provided the possibility of starting additional SPARTAN-III companies in the future.
Shortly after the Path Walkers emerged as a new threat and the resurgence of the Covenant was on the brink of war with the Interspecies Union, the Office of Naval Intelligence decided to initiate Epsilon Company in 2572. An additional 3000 children from 4 to 8 years old were conscripted and trained the same way as Delta Company. They were deployed in 2580.
When the Covenant was finally defeated in 2588, ONI authorized the creation of Zeta Company shortly before the Interspecies Union was reorganized. This decision had initially come under question by many in the military and outside it, as the third company was hardly considered contributory to the reorganization of the Union. However, this decision had paid off after the occurrence of UNSC Astrophysics Anomaly #47931 in 2604, although whether the creation of Zeta Company was a preemptive response to the impending "anomaly" is unknown to anyone outside of ONI.
In 2564, a group of human miners on Sigma Octanus IV discovered a Forerunner artifact deep underground; it had been set there by a former Covenant species called the Evaniptus who had been hunted down to near extinction after uncovering the truth about the Halo array and relaying the news back to the Covenant. The survivors had hid themselves in Forerunner Slipspace pods encased in small Slipspace-capable vessels. They had also left a "beacon" device near Côte d'Azur, which could only be activated by a Reclaimer and would send a trio of the space vehicles to Earth. When one of the miners touched the artifact they had found, it launched the vessels of three Evaniptii (Chak'turr, Fal'ark, and Ma'nar) to Antarctica. The first designated contact they made with humanity was when they were found by a team of Spartans and were later brought to ONI. While the Evaniptii were taken out-system with a team of Spartans and a ship full of soldiers to locate more of their kind, their arrival on Earth and other relevant details were covered up. The ship had returned in 2568, with no trace of the Evaniptii. No one outside the ship crew, except a very few select ONI officers, had knowledge of what had transpired over the four years, and the next contact with the Evaniptii would not be until 2577 when Chak'turr was found in the company of Itzia-D102 while Phoenix Team had been on a mission to locate the Evaniptii.
"Right now, the worst thing the rebels can do is to attack us. To them, the prospect of kicking the UNSC while it's down may a good one in foresight, but we still have enough forces to turn any attack into a bloody slaughter on both sides. And they do know that if they are responsible for destabilizing the only power keeping humanity in one piece, they would consequently be responsible for the eradication of humanity itself. I wouldn't worry about any rebels attacking our colonies, so it would be appreciated if you shut the hell up and stop causing panic among the people by suggesting anything of the sort."
―Chairman Locke to an opposing party during a political debate
Humanity had little to no conflicts from 2553 to 2555. The anticipated rebel attack did not occur at all; Locke had been one of the few people to have predicted that it would be so. However, the Sangheili had been forced to deal immediately with the countless factions that had broken away from the Separatists and try to maintain the most influence over their species. Over time, the factions had either been put down or combined with the one that was steadily gaining the most power, the Fallen. Several incidents between the Separatists and the Fallen occurred from 2554 to 2557, raising tension between the two main sides on Sanghelios. Although it ended with the death of the Fallen's first leader, Atsu 'Hidal, neither sides publicly acknowledged his assassination, but animosity continued to grow, dividing the Separatists and the Fallen as if they were separate species. War would finally break out between the Fallen and the Interspecies Union in 2559, under the command of the second Fallen leader, Isto 'Vadum.
Humanity had their first re-encounter with the Covenant in 2556, although they had been isolated from the Covenant remnants since the Battle of Installation 00 and had deferred to the command of con-human Forerunners after making first contact at the Ark. While on a mission to rescue Dr. Halsey and her Spartans from the shield world of Onyx, Felix-116 and accompanying UNSC forces had pitted themselves against the Forerunner-Covenant force, killing the Forerunner leader, Oberion the Great. The events that followed were reported to ONI by Felix and classified as top-secret, eyes only. One known event was that there was a final battle between the Interspecies Union and the Forerunners at Antarctica, Earth, ending with a strategic Union victory and any surviving Forerunners leaving the system after imparting the Union with tier-1 technology.
Shortly after the Fallen declared war upon the Interspecies Union in 2559, Isto 'Vadum ordered the kidnapping of hundreds of Sangheili newborns. He quickly brought them to Earth and caused a series of incidents which not only led an ODST to believe he was responsible for the deaths of four fellow soldiers, but also caused Separatists at Sanghelios to take into custody an entire UNSC force that was aiding them at the time. Only the timely intervention of Autel 'Vadam helped resolve both situations and prevented the breaking of a delicate trust that had been carefully forged between humanity and the Sanghelios for the last six years.
The Fallen, however, had not been defeated. Even with the death of Isto, they continued to gather strength under the authority of their most cunning leader yet: Urei 'Cazal. In contrast to Isto's deceitful tactics, Urei stood by his honor and values when carrying out his plans. Still, he often bested the Separatists on the battlefield and off, and even with the UNSC aiding the Separatists, he remained steadfast in maintaining power and hope within his followers. Being part of the Fallen since its formation, he had still managed to sustain his pretense of being on the Union's side even after he was appointed as the leader of the Fallen in 2559. He was never exposed as a traitor, but willingly chose to reveal his true colors in 2564 after finding no more reason to play the double-agent.
As every passing year racked up more victories for the Fallen, the UNSC feverishly awaited the deployment of their highly-anticipated SPARTAN-III Delta Company. Finally, in 2568, Phoenix Team was sent to Sanghelios. Commanded by infamous Wings-D339, the tables were quickly turned as the Fallen suddenly began to lose the upper hand to a team of five Spartans. After a few months, the Separatists were looking at the possibility of not only a victory against the Fallen, but even the chance to force them into disbanding. And on February 28, 2569, Phoenix Team delivered a final assault that wiped out the Fallen's headquarters and everyone inside it. Urei, the only survivor, escaped from the ruins and disappeared for over a year before he would re-surface as the leader of the Path Walkers.
Initially a very small group of Sangheili that had broken away from the Separatists as early as 2554, the Path Walkers had averted the attention of the Interspecies Union and slowly gathered numbers over the decades, preferring to avoid conflict and roaming the galaxy for signs of tier-1 technology, with the hope of finding a way to take the Great Journey they still believed in. In 2565, they found a former Forerunner planet named C329t (UNSC designated Beta-14) far from UNSC space and established a headquarters there. They collected numerous Forerunner artifacts and began building a formidable collection of technology. When Urei, who had pretended to be part of the Path Walkers as well as the Separatists, returned to them in 2569 after the destruction of the Fallen, he had already achieved a high rank among them and soon took leadership. Although he held no belief in the Great Journey, he successfully manipulated his new followers into carrying out his orders.
The Path Walkers remained undisturbed until they were located by the Interspecies Union in 2570. A large UNSC force was sent to Beta-14 along with a research team to negotiate with the renegade Sangheili and find out more about the planet. Although the negotiations were at first peaceful, a pair of mercenaries, Simon-G294 and David Kahn, soon abducted one of the Path Walkers, Moru 'Ostal for a ransom of ten million credits. Taking the chance to blame the UNSC of treachery, Urei tried to have the negotiating team captured and sent his Sangheili to attack the humans, soldiers and scientists alike. The mercenaries fled Beta-14 and the Union was forced to send in Separatists to aid the UNSC forces. The situation worsened when the allied Union soldiers scrambled to find the scientists and researchers that were caught in the open from being killed; not long into the fighting, Simon killed a SPARTAN-III from Delta Company and escaped the planet with Kahn and Moru, exterminating any chances of reconciliation between the Interspecies Union and the Path Walkers. Lacking the sufficient numbers to overwhelm the Sangheili by planetary force, and reluctant to make orbital attacks on Beta-14, the Union pulled out of the system. Soon afterwards, Urei urged the reluctant Path Walkers into war with the IU.