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Major Grade One.png This article, Swarm War, written by StoneGhost, was voted as the Best Event of 2010 in the Third Annual Halo Fanon Wikia Awards.

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20101106171422 This article is part of Swarmverse, an inactive expanded universe made defunct by newly created canon material.
Swarm War
Montage small.png Clockwise from top left: UNSC troops and armour engage the Swarm; Theran Soldiers defend their position; a culled world is bombarded by Swarm fleets; UNSC Marines come under attack; the Battle of Thera; Swarm forces bombard Britannia

8th April 2633, Battle of the Antaeus Nebula


2678, Battle of Installation 07


Milkyway Galaxy

  • Allied forces pyrrhic victory
  • Extinction of The Swarm (assumed)

nations of the Unified Coalition of Governments

The Swarm

  • The Hive
  • Queen (speculated)
  • Over 400 million warships
  • Several billion starfighters
  • Over 360 billion military personnel

Unknown; speculated to be in the trillions

  • Vast majority of military units (95%+)
  • 850 trillion sentients (95%+ pre-war population)
  • 65 million worlds

Total (assumed)

"Ancient evil, from before and beyond the universe itself. A nameless, terrible thing, soaked in the blood of a billion galaxies- the most feared thing in all the Cosmos. And nothing could hold it or stop it, or reason with it; one day it would just drop out of the sky and tear down your world."
―An excerpt from an ancient Theran proverb, origin unknown

The Swarm War, also known as the Black Century and the Great War, was a devastating pan-galactic conflict that arose after The Swarm, a violent insectoid species, invaded the galaxy. The war engulfed the entire Galaxy for a span of forty five years, during which period the Swarm slowly but unstoppably pressed nearer the galactic core, invading and capturing their populations and leaving a trail of razed planets in their wake. The Swarm, dependent on organic hosts for survival and masters of biotechnology, overwhelmed the combined efforts of the Unified Coalition of Governments and its constituent nations, emerging victorious from battle after battle due to superior tactics, efficient biotechnology and sheer numerical superiority. Although the Swarm War began in earnest in 2633, in actual fact first contact occurred on the planet of Radiance in 2557, a remote colony on the rim of the galaxy. The Swarm wiped out the population and then left, leaving no trace of their nature remaining for the colony's discovery nine months later. The Swarm observed the galaxy for a over a century before launching their all-out assault, slowly encroaching into the heart of the galaxy. The war cost the lives of over 850 trillion sentient beings and devastated or destroyed over sixty five million worlds. The galaxy did not recover from the Swarm War for at least a millennium after the defeat of the Swarm, though some historians its effects could be observed for much longer afterwards than this.


The origins of the Swarm War lie mainly in the Swarm's reliance on organic hosts for reproduction. Incapable of producing offspring on their own, their reproduction was dependent on implanting genetic material and fertilised eggs into (preferably living) host beings. The Swarm had travelled millennia between galaxies from their home one; their reasons for this mass exodus are still unknown, though speculation points to the depletion of that galaxy's prey species. Surviving in stasis with a few select individuals known as 'Keepers' watching over the vessels, the fleet of billions of vessels arrived in the Milky Way galaxy weakened and in need of both life forms for reproducing and food, the Swarm encountered several uninhabited planets, wiping them clean of animal life, before coming on the Allegiance outpost of Radiance. Over the next hundred years or so the Swarm remained in the shadowy realm on the periphery of galaxy, consolidating their strength and preparing for the galactic invasion to come. The Swarm's ultimate intentions in the galaxy seem to have been to consume all it could, leaving the galaxy devoid of life while growing themselves in strength and numbers, before moving on to another. It is unknown how many times previously the Swarm had journeyed between galaxies if at all.


The Swarm War was the first to see all known races of the Milky Way Galaxy unite to face a single foe, although this did not occur right away. The war saw several large and numerous smaller factions all pitted against the Swarm, which was numerically superior and arguably technologically so in addition to this. Despite being technically part of one united faction, the various nations did not cooperate to a large degree until the scale of the Swarm threat became clear, and operated as allied, though separate, entities.

Alliance of Sangheili Clans

The Alliance of Sangheili Clans was the governing body of the Sangheili race. It was formed in March 2553 on Sangheilos, and was based on the foundation of the Covenant Separatists. By the time of the Swarm War the Sangheili encompassed several million worlds, many with multi-species populations. During the war, the Sangheili's military was near constantly active against Swarm forces, not only in their space but in other territories as well. Sangheili space was heavily encroached into by the Swarm, with heavy civilian casualties and planets lost. In particular, the Sangheili as a whole could not understand the Swarm's constant hunger for sustenance or its violent hive-based society, and therefore did not meet them on the battlefield with the same respect that they had for past enemies. The Sangheili and many other former Covenant species shared an extremely close bond during the war, with the possible exception of the Jiralhanae-Sangheili resentment, and all referred to the Swarm most commonly as the abomination, in a similar manner to the Flood.

Antarean Commonwealth

Democratic Unggoy Alliance

The Democratic Unggoy Alliance, or DUA, was the ruling body of the Unggoy species. Seeing the Swarm threat, the DUA began to fortify their worlds and prepare for the Swarm's attack, rather than pro-actively involving itself with the war before it had reached their borders. When the Swarm reached their doorstep they quickly overwhelmed the Unggoy's defences, devastating the DUA's civilian populations. From this point on Unggoy forces, spatial fleets in particular, played a more prominent role in the war. Most Unggoy ships were jointly crewed with Yanme'e as well, and some operated alongside Sangheili as well.

Kig-Yar Republic

Despite not being directly in the line of attack during the early years of the war, the KYR saw that the Swarm was a major threat and as a result, actively involved itself with combat. The Kig-Yar's vast fleets of fast, light vessels were most commonly seen aiding UNSC and Sangheili forces in various battles though operated more or less independently in the Kig-Yar's own attacks on the Swarm, which it mounted frequently during the war's first century. The Kig-Yar Republic, however, took heavy losses when its territory was invaded despite large scale preparation and support from other allied factions. From this point on the Kig-Yar's role in the war was diminished, although not totally insignificant. There was virtually no contact with the Kig-Yar for the last forty years of the war and, like the Unggoy, their civilisation was ravaged to a point where ruling organisations could not keep control, and the state descended into anarchy whereby it degraded itself further.

The Swarm

The Swarm was a vicious extragalactic insectoid species that depended on organic incubators for reproduction. Coming in three known life stages with various different forms, the Swarm besieged the known galaxy with massive numerical superiority, stunning tactical moves and advanced biotechnology. The Swarm, although taking colossal losses before the end of the war, never really seemed to be affected by this, mainly due to its huge relative size. The Swarm entered the galaxy on a vector taking them through Allegiance space, once there exploiting neutral zones and assaulting and eventually breaking through to other nations.

The Royal Allegiance

The Royal Allegiance was a technologically advanced faction of near humans, or Therans. Despite inherently despising war the Allegiance maintained a substantial and modern armed forces as a result of centuries of turmoil following the Human-Covenant War, although these numbers were slashed in the mid 26th century. Bearing the initial contact at the Antaeus Nebula as well as most of the first attacks, it was the Allegiance that discovered the true extent of the Swarm threat and surmised that they could not deal with it alone. Being the largest faction in terms of territory, the Allegiance took the heaviest losses in terms of military, civilians and actual planets fallen.

The Order

The Order was a race of near-humans genetically engineered by the Forerunners to be the next guardians of the galaxy from external threats, once the Forerunners had departed. Tasked only with this, the Order kept out of galactic affairs until later into the Swarm War once it became apparent that the fate of the galaxy was not just in danger but imminently so, despite the efforts of the combined races. Previously using their advanced technology to remain hidden, the Order revealed themselves and joined the assault on the Swarm, temporarily raising morale. Though the Order had not fixed territory in space, their numbers took heavy losses during the war and afterwards, they once again faded into obscurity. It is unknown how many survived, but it is known that their efforts during the War stalled the Swarm for at least two decades.

Unified Earth Government

The Unified Earth Government, or UEG, was the ruling body of the Human race. Seeing major action during the Swarm War, the UNSC, the UEG's military branch, was the second force to engage the Swarm after the Royal Navy. Along with the Therans and the Sangheili, the UEG fought most of the Swarm War's battles and took the heaviest losses. The UEG played an important role in the eventual defeat of the Swarm. Although the UEG's territory was severely encroached upon during the war, hit-and-run and guerrilla tactics helped the UNSC survive when it was at its weakest. The UNSC was one of the last factions to actively mount resistance against the Swarm and was recognised as imperative in their eventual defeat, despite catastrophic losses.

Unified Coalition of Governments

The Unified Coalition of Governments, or UCG, was set up following the Human-Covenant War aimed to facilitate cooperation in galactic law and security, and the achieving of galactic peace. During the Swarm War it increasingly gained military control from its constituent nations, reluctantly handed over by them, to enable closer cooperation between armed forces.

Union of Jiralhanae Tribes

Being physically on par with many swarm types, the Jiralhanae saw very widespread action against the Swarm, both in their own territory and protecting others, particularly the UNSC, Kig-Yar and Unggoy. The Jiralhanae race saw the loss of their homeworld and many of their core worlds, and took heavy losses more specifically in ground combat, as races such as the Therans and Sangheili tended to operate the spatial defence while the Jiralhanae took the ground combat alongside the UNSC.

Ve'nek Dominion

The Ve'nek Dominion was a government formed by the Ve'nek species. The Ve'nek, sharing a close relationship with the Allegiance and being geographically close, became involved in the war relatively early. The Swarm began to encroach into their territory and although they managed to slow this considerably, they took heavy losses. Towards the end of the war, with their territory virtually gone, the Ve'nek survived by wandering space in colossal generational ships, rarely becoming involved in actual combat other than when they were engaged directly.

Yanme'e Conglomeration

While remaining an independent government, the majority of the Yanme'e's military was combined with that of the Unggoy and the Sangheili. Although their homeworld was nearly destroyed, Yanme'e territory remained largely unravaged, although occupied, by Swarm forces.


Early War

First Contact

The first confirmed encounter with the Swarm by any race was in 2557, when they happened upon the UNSC outpost of Radiance. The colony was a relatively small scientific research outpost on a frigid planet, isolated and largely unknown. Several Swarm ships assaulted the colony, and, while quickly smashing through the spatial defenses, were pressed into a short but bloody battle with UNSC ground forces. Ultimately this proved futile and the Swarm overwhelmed the defenders, thwarting a desperate attempt to warn the galaxy at large. The Swarm then moved on, having tasted the rewards invasion of the galaxy could bring and hungry for more blood. Following this, they slowly and covertly built up their strength, all the while observing conflict in the galaxy slowly weaken individual factions. The UNSC did not discover the remains of the Radiance outpost until three months later, by which time the Swarm were gone and would not appear on the galactic scene again for over fifty years.

Second Encounter and Early Years

Main article: Battle of the Antaeus Nebula

More than a century later, in early 2633, a number of disturbances occurred near the Antaeus Nebula, prompting the nearby UNSC, Allegiance and Ve'nek to investigate. on 25th January, a small UNSC freighter was reported missing, followed by an Allegiance survey shuttle on 12th February, and a Ve'nek passenger liner on the 27th. This passenger liner, bound for Acheron, had among its passengers several high profile politicians. This, combined with the other disappearances, forced the three governments to begin searching for not only the vessels but the potential cause of the disappearances. The cause of these happenings, unknown to the UNSC, Ve'nek or Allegiance, was the return of the Swarm to within the boundaries of the galaxy. Vessels they happened upon were stripped of their crew and devoured, leaving only traces of the ships which they destroyed afterwards.

The first, inevitable confrontation occurred on April 8th, when a group of three of Triton-class destroyers detected an unidentified group of vessels while in slipspace. The commanding officer, then-captain John Bradley, launched a spy drone from his vessel, Watchman, which was detected and destroyed by the unidentified vessels, beginning the Battle of the Antaeus Nebula. Bradley demanded identification, but the replying transmission- a rapid cacophony of hisses, clicks and screeches- was indecipherable by the ship's AI. In the ensuing battle, two of the three Triton-class vessels were destroyed, with only the Watchman escaping, although the Allegiance vessels dealt heavy casualties on the nine enemy vessels.

The pace at which the Swarm stepped up its incursions into the galaxy took many by surprise; following the first engagement, the Swarm invaded four more systems; Acheron, Chiaras, Crolun and Jana over nine separate battles. The following year, the figure was more than double this, with five systems alone being completely conquered by the Swarm. After the first ten years UCG losses were staggering; over three hundred worlds lost to the Swarm in total, and over three hundred million casualties both civilian and military. Yet despite this, and the massive re-armaments and scaling up of military projects, the Swarm continued to push into the galaxy, breaking through line after line of defensive fortified worlds and drawing ever closer to the inner planets. Frustrating the war effort was the fact that, after defeating defending forces of a planet and consuming its population, the Swarm would bombard it from orbit, making sure to destroy every single structure and preventing UCG forces from reoccupying it. While the UCG achieved some major victories, their superior technology and weaponry could not match the Swarm's morale-obliterating ferocity, astounding tactics or their biblical numbers. The Swarm systematically began forcing the UCG further and further back and, although the speed of this seemed electric, it was nothing to the Swarm's stepping up of their attacks from the mid 27th century onwards. By 2645, the Swarm was launching massive, concerted attacks against the UNSC, Allegiance, Ve'nek Dominion, Antarean Commonwealth and Alliance of Sangheili Clans. Worlds were falling at a precipitous rate, and Allied stands on dozens of planets were simply brushed aside. The war was declared officially a Galactic War, with Swarm incursions occurring regularly. By 2650, almost all of the Galaxy's outer rim worlds were lost to the Swarm, which encompassed both many large population centres and hundreds of thousands of raw material-producing worlds. This period also saw the undertaking of several large scale operations against the Swarm such as Operation: BRIGHT LIGHT, which attempted to evict large numbers of Swarm fleets from the galaxy.

The first few engagements of the Swarm War took place in Allegiance territory; thus, the first major battle followed this. After the location of Acheron, a major outer rim world, was learned by the Swarm, the Allegiance prepared for a major offensive. On the 2nd February a large Swarm naval force entered the system, and engaged the defending Navy orbiting the planet. The following battle was protracted and bloody, with the Royal Allegiance Navy both attacking the invader's vessels and preventing enemy ground forces from landing. Eventually they succeeded in both after heavy losses on both sides, the Allegiance making manoeuvres that compensated for their inferior numbers. Following the battle, the Allegiance increased their armed forces in surrounding systems and began preparing for a counter-offensive to hit back at the Swarm and halt their advance early.



Second Wave

Defensive Measures


Kig-Yar Incursion


Galactic Threat

Operation: DENIAL


The term 'Mid-War' was used to describe the period between 2640 and 2655, which roughly represented the period of time in which the Swarm began its assault on the Galaxy's Mid Rim. 2651 was also the year of Operation: RECLAIMER (also referred to as the Lost Offensive), a combined and large scale offensive by a number of the Allied nations. The sheer scale of the assault took the Swarm by surprise, and the Allies gained back hundreds of thousands of worlds from them over a six month-long campaign. Despite this, not one of the worlds possessed anything worth taking back; all had been bombarded from orbit and were devoid of population, structures or raw materials. From this point on the Allied strategy shifted from reclaiming lost worlds to successfully defending them in the first place. Following this, already considerable defences were stepped up further, though the Swarm countered this with even greater numbers. This period saw the Swarm's invasion of, and eventual devastation of, the Galaxy's Mid Rim which, referred to as the 'Green Rim', was the source of much of the Galaxy's agricultural produce. Continual Swarm encroachment put further pressure on surviving worlds, even though populations were in decline due to monumental military and civilian losses. The Galaxy's military forces reached a peak at some time during this period; from this point on, mass conscription and forced military duty began to be outstripped by battle losses (and at an increasing rate). Historians cite the end of the Mid-War period as the Swarm's assault on the inner colonies, in 2655.

Late War

The late war saw the Swarm's assault on the Galaxy's most densely populated regions including its largest population centres outside the core. It also saw the beginning of a loss in cohesion in some governments as they were pushed to the brink of annihilation, with civilisation in some parts giving way to lawlessness, anarchy and barbarism. Desperate, last-ditch measures such as Project GATEKEEPER and Project VIRAL were enacted to attempt to save what was left of the Allied territories, which slowed although did not halt the Swarm's advance. between 2655 and 2670, the Swarm ravaged hundreds of thousands of inner colonies and, in 2670, launched its first attack on a core world, Britannia.

Assault on the Core

Last Battles




The character meaning 'Swarm War' in the Theran language.

In terms of social impact, the Swarm War was remembered for many centuries following as a near-cataclysmic event. The War had a lasting impact on social memory. It was seen by many in the galaxy as signalling the end of the 'Golden Age', the name given to the period of relative prosperity and development preceding the war from the early 2600s until the start of the war. Many across the galaxy regarded the event as a watershed moment, in that the galaxy as a whole, regardless of species, had been presented with a potentially all-consuming enemy, the likes of which had not been seen since the Forerunner-Flood conflict. The commonly held belief was that such a serious, existence-threatening war threw the small conflicts and skirmishes between 2559 and 2620 into stark contrast, effectively shocking the galaxy into a deep-seated opposition to conflict, even in warlike races such as the Jiralhanae.

The social trauma caused by unprecedented rates of casualties manifested itself in different ways, which have been the subject of subsequent historical debate. The experiences of the war led to a collective trauma shared by many from all participating nations. The optimism of 'The Golden Era' was destroyed and those who fought in the war were later referred to as the Lost Generation. For years afterwards, people mourned the dead, the missing, and the many wounded. Many warriors returned with severe trauma, suffering from psychological issues that often took years to manifest themselves. A lucky few returned home with few after-effects, however their silence contributed to the conflict's growing mythological status. In the Royal Allegiance and the UEG, mass-mobilisation, large casualty rates and the collapse of the colonisation age made a strong impression on society. Society post-war was burdened with rebuilding the galaxy's shattered worlds whilst coping with the loss of billions of sentient beings to a terrifying, seemingly unstoppable, all-consuming enemy. This contributed to exceedingly low public morale immediately following the war, which lasted for several decades after the war.

The Swarm War became such a common term in every day language that, in the Theran language at least, it acquired its own character, as occasionally happened to represent phrases instead of spelling them out with traditional characters. This character remained in use until at least seventeen centuries after the war, though by that time it had lost its original meaning and instead was used as an analogue to what would be literally translated to 'the eternal darkness' .


The economic consequences of the Swarm War were immense. Private businesses were wiped out, either physically destroyed, losing business or having their assets commandeered for the war effort. Food production, particularly after the mid rim of 'Green Worlds'- that produced much of the galaxy's food- was ravaged by the advancing Swarm. Rationing was introduced throughout most territories, mainly of food and materials as energy could be easily obtained. Items vital to the war effort, such as metals and gravitational compressors used for armour, electrical equipment and other valuable materials, became more valuable and rare as the militaries increased their usage. Growth in manufacturing industries, particularly munitions, weapons and warships, enjoyed a boom as production skyrocketed, though this was largely negated in the later war where the Swarm hit these industries hard. All factions lost large portions of their productive capability over the course of the war. Other, mainly civilian sectors such as ground construction (other than military) and services were largely neglected as funding was redirected to more vital projects. Large scale shortages of workers resulted in part from heavy civilian casualties, as well as conscription and lack of funding for training schemes. Merchant vessels and crew suffered massive casualties, severely affecting trade and commerce both between systems and territories. Large scale nationalisation was introduced as states took control of resource and personnel allocation, housing, banking, transport and food. Workers were often called up from civilian life, either as part of wide scale conscription or allocated to vital roles such as munitions production. The economy post-waar was not only in a state of shock and disrepair, it was so that society was near the brink of total anarchy, though opinions to the nature and scale of this remain diverse.