The Empire, alternatively known as the First Imperium in historical circles, has it's roots in United Nations Space Command, the military wing of the now defunct United Earth Government. With the resulting dissolution of the United Earth Government as a result of political pressure from the "Blue" movement in June 2567 and the chaos that followed it's absence, United Nations Space Command remained active and ordered martial law on all UNSC-controlled colonies until an interim provisional coalition government could be established with protestors and negotiations would begin. However, those negotiations never really took place as an unknown Lieutenant General from the UNSC's Marine Corp took control of the organization in a coup backed by small elements of his namesake organization. This leader, his name still unknown to this day, stormed the former United Earth Government Public Relations Center in New York, New York on Earth with elements of the Marine Corp's ODST segment where negotiations were set to begin and stopped the peace process entirely. The following occurred immediately afterwards; any UNSC military leader in the building was imprisoned as was the political leaders from the protestors movement who had attended the summit with the hopes of finally ending an Earth-based human government. This Lieutenant General subsequently garnered for himself the title of Emperor, and re-organized the crumbling remnants of Humanity's first universal government into what is now known today as "The Empire."

The Empire's beginnings did not remain as smooth as it's takeover, however. Numerous planetary governors in the UNSC, installed after the UEG's collapse and charged with keeping the peace, were quick to capitalize on the early instability of the Empire. Nearly all of them were high-ranking military officials, and thus retained high amounts of loyal soldiers, ships, and ordnance. These men and women took the position of warlords, seceding away with vital planets such as Mars, Victoria, Mamore and others. The Emperor subsequently re-organized the UNSC's military elements into the Imperial Navy, Imperial Marine Corps, Imperial Office of Naval Intelligence, and ordered Dr. Catherine Halsey's SPARTAN program revived and restarted. He then set about destroying each warlord piecemeal; the first to fall was Mars, being it was a fortress world at Earth's doorstep. The other planets who had broken away quickly followed suit, and those who chose to surrender were summarily executed in public areas as an example of what happened to traitors in the new regime. By 2570, nearly 90% of all self-proclaimed independent warlords had been exterminated and the Inner Colonies had been brought back entirely under Imperial control. By 2571, the remaining 10% had been exterminated as well, leaving only the same Insurrectionists who existed in the Outer Colonies just like before the United Earth Government had collapsed. To this end, the Emperor selected elements of the Imperial Military, still the UNSC in all but name, to seek out and eliminate these rebel elements. 2571 also marks the first time Imperial soldiers were identified as having crimson and red coloring added to their armor. The "Blue" political movement went underground immediately as it's leaders were systematically abducted and never heard from again.

The next year went extremely well for the Empire. Military research and development went up nearly 50%, primarily funded by taxation of Outer Colony agri-worlds and mining worlds. Relations with the Sangheili species and it's lesser servant species were renewed, ensuring a strong ally in the event of another interstellar conflict, and recruitment for the Imperial Military went up 77%. The SPARTAN program was accelerated and the formula for creating the perfect soldier perfected; the end result was the Spartan-IV, more numerous and robust than all three of their preceding classes. Equipped with updated variants of the MJOLNIR Powered Assault Armor suit, more specifically Variant VIII, these Spartans began to be churned out at first in regiments and later on at division strength. Although still not nearly as numerous as the men and women of the Marine Corp, their presence became an added reminder of the power of the Empire, and their official designation as a group was the R.E.D.D., or Royal Enforcer Deployment Division. Officially attached to the Imperial Office of Naval Intelligence, the R.E.D.D. answered directly with full loyalty only to the Emperor, taking an oath of service until death directly to him rather than to the Empire as a whole to ensure they would remain faithful. However, the new Spartan program was not without flaws. The extent of these defects would not fully be realized until 2573, when the "Blue" political movement re-emerged from hiding in a militant manner as the Brotherhood Legion of United Exiles and Spartan-IVs and Marines alike would turn their backs on their oaths.

The resulting rebellion caused by the Brotherhood hit the Empire like a firestorm in a room full of highly flammable material. For quite sometime Imperial injustice had become rampant with public executions, over-taxation, corrupt officials and a myriad host of other problems. The Brotherhood, no longer in hiding, capitalized on this when it hacked Inner Colony Courier's news stations and flooded human-controlled planets with evidence of Imperial cruelty in February 2573. Public opinion of the current government automatically went south, and riots and crackdowns occurred everywhere as these atrocities were brought to light to the more modest elements of society. The immediate effect was legions of citizens flocked to enlist to fight for it's cause; the secondary, and in many opinions the more serious effect, was whole professional divisions of Imperial Marines, regiments of Spartan-IVs, and whole naval fleets flocking to the Brotherhood as well after seeing the severe corruption and war crimes of certain areas of the Empire and Imperial Military. Overnight, the Brotherhood became a full-scale Insurrectionist movement with a serious desire to see the end of the Empire before the turn of the decade. Despite such mass-scale defections and internal problems, however, the Empire still maintained a sizable military force and as such staved off any threats of immediate invasions by virtue of the very men who had defected who knew the true extent of the Imperial war machine.

However, the Empire severely misunderstood how much of a threat the Brotherhood was once their enemy was made known to them in opening engagements, and it's highest military leaders chose to treat these "Blues", the derogatory term for them, as common rabble who had no true organization or martial skill. When Victoria became the first planet to re-secede from the Empire and became the Brotherhood capital in April 2573, the Empire sent a massive force comprised of the Imperial Navy, Marine Corp, and the R.E.D.D. to the colony with the intention of "curbing this autistic proletariate uprising once and for all." Upon arrival out of Slip Space, however, the armada was obliterated by a mixture of defected Imperial navy ships and rebel ships still in operation from the Human-Covenant Era and beyond. Simply caught unprepared and unready for such a sudden blitz, nearly 40% of the fleet was destroyed in the first hour of the naval engagement and another 30% was boarded and seized by Brotherhood forces, who proved to be remarkably well-organized for only a few months preparation out in the open (it was apparent however this defending fleet relied heavily on defected professional Imperial military elements and not uniquely rebel units). The remaining ships that did escape the initial engagement proceeded with the operation under the foolish orders of Imperial High Command (IMHC) Outer Colonies, and landed their ground forces planet side. These units, comprised of the Imperial Marine Corps and the R.E.D.D, initially fared well until what remained of their naval fleet was destroyed two weeks after landing. After another two months and lacking supplies, these planet-side forces surrendered entirely. Subsequently, the entire brass of IMHC Outer Colonies was executed for incompetence.

The remainder of 2573 through 2581 was not kind to the Empire. In early 2574, the Empire sustained another crushing loss at Harvest, and lost another major deciding engagement in 2577 when they tried to invade and take Victoria a second time. All the while, the Brotherhood's power grew and grew while the Empire continued to decay and lose ground in the Outer Colonies until it maintained control over only a fraction of Outer Colony planets. It was only when reconnaissance ships discovered Installation 03 in 2581 and the Empire subsequently landed forces on the Halo Ring that the tide began to turn when reverse-engineered Forerunner technology began to pop up in higher class echelons of the Imperial Military and they began to regain the upper hand in conventional engagements against the Brotherhood. Weaponry, better technological systems such as improved FTL engines, etc. improved the efficiency and became the standard of the Imperial Military, reviving it's sagging war economy. The effect was not immediate, but by 2586 with Forerunner technology and more competent leaders the Empire had re-surged to take back previous Brotherhood gains on the edges of the Inner Colonies and began to move on the offensive. It successfully staged three defenses of Reach, preventing Brotherhood access to Earth, and ironically annihilated a Brotherhood armada en route to Mars as well as one en route to Sigma Octanus VII. This trend of one-sided victories has not continued, however; currently, it is on an even keel with the Brotherhood in terms of technology and military strength after the Brotherhood discovered the location of Installation 03 and captured upgraded Imperial technology in recent engagements.

Since 2590, the Empire has regained a position similar to what it was before 2573, albeit at a very diminished capacity. Despite the amazing number of setbacks and defeats suffered at the hands of the Brotherhood, the Empire has one thing going for it still: establishment. The Empire still has more numbers, more resources, more technology, and more allies in the form of half the Sangheili race, the Unggoy and the Mgalekgolo. However, it's inability to adapt to such an enemy that can fight both conventionally and unconventionally at the same time may prove it's undoing. Only time will tell whether the juggernaut that is the Empire will be able to even touch it's adversary in any major way. Currently, the Empire is in a balancing act between attempting to acquire Forerunner technology and fighting off the Brotherhood.