Forefather War

"Great ships cloaked in the darkness of the void emerged, bringing forth an incomprehensible enemy to all who inhabited the Galaxy."
- Observations of The Watcher.The Forefather War, otherwise known as the S'southi Invasion of the Galaxy, the Alliance War, the Great Selath or the War of Galactic Resistance was a major conflict within the Milky Way Galaxy, with the combined forces of the major governments in the known galaxy resisting the invasion of the S'southi under the Forefathers.
==Background==
Prior to the Forefather War, several attempts were made by the Ministry of Intergalactic Affairs, a branch of the Lights of Purity, to contact a number of supposed Forerunners living within the Andromeda galaxy. The combined efforts of the Ministry of Divine Knowledge and the Ministry of Intergalactic Affairs lead to the mounting of the Void Journey, in which a Forerunner deep-space exploration vessel from Propriety was used in an attempt to directly contact the Forerunners. Upon the arrival of the vessel, the Forefathers exited their centuries of hibernation and amassed a S'southi army. 
==History==
===Opening Engagements (February-April 2560)===
The S'southi Armada, using highly advanced organic-based slipspace technology, arrived at the edge of the Milky Way Galaxy in weeks. As Humanity and the Krythenans were embroiled in their own conflict, the S'southi saw fit to neutralise the largest threat, and attacked the Lights of Purity and various other Remnant factions, which where taken by surprise and suffered massive losses in the opening weeks of the invasion. 
As soon as news of the invasion reached Humanity and the Krythenans, both states ended their hostilities and formed the Galactic Alliance in order to counter the S'southi. Membership of the Galactic Alliance only grew as the S'southi got deeper into Covenant and Krythenan space. The S'southi fleet abandoned their attacks on the Lights of Purity and launched an attack on the Krythenan Empire, where they were countered and decisively defeated at the Battle of Matun'ds. 
Following the destruction of the initial S'southi invasion, the threat had seemingly passed, though the Galaxy remained on high alert as they dealt with guerrilla stragglers in Krythenan space. The main invasion would begin with the arrival of the S'southi Armada in early May.
===Open War (April 2560 - January 2562)===
====Outer Worlds Campaign====
"We thought the war ended at Matun'ds."
- Cobadarama upon learning of the new armada.Galactic Alliance Intelligence discovered the existence of the S'southi Armada prior to it's invasion of the Galactic Frontier. A large coalition fleet was assembled to carry out OPERATION: UNITED FRONT, a planned surprise attack on the S'southi Armada before it could bring the war to the doorstep of the Alliance. This attack was executed in early April of 2560, and was a decisive S'southi victory. Despite the initial shock of the surprise attack, the alliance had severely under-estimated the S'southi following their defeat at Matun'ds and as such were devastated after the S'southi were able to retaliate.
Following the victory in OPERATION: UNITED FRONT, the S'southi began a campaign of destruction throughout the outer layer of colonies and settlements in former Covenant space. Despite putting up heavy resistance on each planet, the Galactic Alliance ultimately failed to hold off the S'southi and the Outer Worlds Campaign ended up as a major success for the invading forces. The Outer Worlds Campaign came to it's apex in the Battle of Polss.
====Guerrilla Warfare====
During and following the Outer Worlds Campaign, a number of Galactic Alliance forces waged an unconventional war of resistance against the S'southi. While most guerrilla cells would be defeated within weeks, a number survived and remained in operation until their liberation.
====Krythenan Campaign====
"They're attacking Krythenan space again. They did this exact same thing last time, attacking another region then turning their undivided attention to the Krythenans. Why?"
- James Coleman's Memoirs.Following their victory in the Outer Worlds Campaign, the S'southi would begin to strike the rim of Krythenan space, waging a brutal war against the urbanized economic centers of the Krythenan rim. The S'southi suffered their first defeat following Matun'ds at the Battle of Khaife. The Battle of Khaife significantly reduced the momentum the S'southi had and allowed the Galactic Alliance to prepare a number of defenses in Krythenan Space.
=====Renewed Offensive=====
Despite the devastating loss at Khaife, the S'southi were not entirely defeated and still fielded a gigantic armada which continued to loom as a gigantic threat to the Galactic Alliance. The S'southi would, in an act of vengeance, attack the urbanised world of Sedath. Their attack, while not particularly devastating to Alliance forces, was devastating to the civilian populace, as the S'southi concentrated their attacks on residential districts and slaughtered hundreds of thousands in the span of a week. Alliance forces evacuated from the planet with a large number of civilian refugees, leaving those remaining on Sedath and the planet itself to the mercy of the S'southi.
Following the Battle of Sedath, the S'southi continued advances into Krythenan space, attacking numerous frontier worlds which had been abandoned in favour of an inner defense grid.
====First Battle of Installation 01 and the fall of the Outer Grid====
"Our defenses cannot hold forever, and they aren't supposed to. We're just aiming to kill as many of those bastards as possible."
- Colonel Devin WeeksOn the eve of a S'southi attack on the defense grid, the S'southi discovered the location of Installation 01 through the usage of the Luminary on Propriety. The ensuing battle of Installation 01 would ultimately be a defeat for the S'southi, but their loss on the installation would be outweighed by their victory in the coming Outer Grid Campaign.
The Battle of the Outer Grid would be, ultimately, a S'southi victory, though the large losses they would take would hamper their future war efforts.
====Fall of the Inner Grid and the defeat of the Krythenan Empire====
"It's over."
- Cobadarama witnessing the Fall of Antis.The Battle of the Inner Grid began immediately following the Battle of the Outer Grid as S'southi forces ramped up their efforts to puncture the defenses. In a similar timeframe to the last battle, it took them six months to breach the defenses, reaching Antis, the capital of the Krythenan Empire, by the 29th of November.
Antis fell on the 30th of November after a devastating battle, and the Krythenan Empire dissolved. Despite the loss of Antis, the S'southi had been weakened by the large amount of casualties they sustained over the course of the battle.
===Invasion of the Outer Colonies (January 2562 - December 2563)===
In the months following Antis, the S'southi mopped up Krythenan resistance within Krythenan space, and would turn their attention towards Humanity. Humanity had not anticipated a S'southi attack on the Outer Colonies to come so soon, which lead to the surprise attack on the Lambda Serpentis system being especially deadly.
====Initial Incursions====
"This is Commander Eddie Salim of the Orbital Defense Platform Hastings, we are under attack! I repeat, we are under attack! They've found the outer colonies!"
- Commander Eddie Salim during the Attack on Lambda SerpentisThe opening battle of the S'southi invasion of the Outer Colonies, the attack on Lambda Serpentis saw the destruction of a large number of Galactic Alliance forces by a relatively small number of S'southi combatants.
Following the attack on Lambda Serpentis, the S'southi attacked the Charybdis System and conquered it decisively. Shortly after this, the glassed planet of Society was occupied by the S'southi.
Shortly after the battle of the Charybdis System, the luminary housing the information required to locate the Great Archives was finally recovered by a joint team from the Office of Naval Intelligence and the now-defunct Krythenan Imperial Intelligence Corps. S'southi spies relayed this discovery to the Forefathers and both sides engaged eachother in the Battle of the Great Archive. Long-time insurrectionist Kayode Adetola alongside the AI construct Cassandra retrieved the information before either side could.
===The Alliance's Final Stand (June - August 2566)===
By June of 2566, the Alliance was close to defeat. Having fought the war constantly for six years, the initial hope that the galaxy could resist the S'southi was fading and victory seemed to be an impossibility. Despite this, a plan devised by Fleet Admiral James Coleman was chosen to be the Alliance's final resort, code-named Operation: SANCTUARY. The operation itself was entirely fabricated and was actually a diversion from the real plan named Operation: RESOLUTE HOPE. 
Operation: SANCTUARY was devised in such a way to be extremely secretive however easily leak-able, with what remained of the S'southi intelligence grid within the Galactic Alliance learning of this "plan" rather quickly. The plan outlined a full retreat with all available Galactic Alliance vessels to the Lesser Ark, Installation 00, with the hope that they could escape the S'southi permanently and renew their civilisations on the Ark. Of course, this was all a fallacy, with the real plan, as outlined in Operation: RESOLUTE HOPE, being the withdrawal of all available Galactic Alliance vessels to the Ark to draw in the S'southi Armada and engage them until the arrival of Installation 01, at which point the GA would withdraw and the installation would wipe out the S'southi Armada entirely.
====Operation: RESOLUTE HOPE====
"This plan isn't just very stupid, it's also very risky. But I like it." - CassandraThe S'southi were deceived, with the Second Battle of Installation 01 and the Battle Over the Ark commencing. After a few days of engagements, the team deployed to Installation 01 was successful in defeating the S'southi forces and reaching the Ark, however Binding Enlightenment quickly learned of their intentions and attempted to halt the firing of the installation personally. He failed, being killed by the Spartans Rose-788, Theo-783 and John-117 alongside the ODST Victoria Theodorides. Galactic Alliance forces withdrew through a portal opened above the Ark and the halo was activated, wiping out the entire S'southi Armada in the process, effectively ending the war.
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==Belligerents==
===Galactic Alliance===
The Galactic Alliance was a united front against the S'southi invasion made up of several autonomous states. It encompassed almost all of the known inhabited Orion and Sagittarius arms of the galaxy., incorporating many races and organisations.
====United Nation Space Command====
The United Nations Space Command was an increasingly aging relic of the Human-Covenant War. Despite affording several rights and autonomy to local governments following years of direct rule during the Great War, the government remained unpopular due to it's near dictatorial stranglehold over politics and the silencing of many political dissidents, especially in the surviving Outer Colonies. The Forefather War was a breath of fresh air for the UNSC, uniting it's dissidents under the UNSC flag against a common enemy, similar as to what had happened to the Insurrectionists during the Human-Covenant War.
The UNSC served as an important backbone for the Galactic Alliance, with it's new-model fleet having been produced in massed numbers alongside re-activated reserve units from the Great War it's navy constituted a large fraction of the Galactic Alliance navy alone. Another important contribution was that of the SPARTAN program, with surviving SPARTAN-II and SPARTAN-III supersoldiers proving especially valuable in the war, alongside the newer generation SPARTAN-IVs.
====Krythenan Empire / Reformed Krythenan Empire====
On the onset of the Forefather War, the Krythenan Empire was one of if not the most important strategic asset to the Galactic Alliance, a fact which made it's dissolution following the Fall of Antis all the more devastating. Unlike the Covenant Remnant factions and the United Nations Space Command which made up the other two major thirds of the Alliance, the Krythenan Empire did not use archaic Human-Covenant War tactics and were not bound to them through tradition. Having fought an asymmetric war for almost two hundred years prior against eachother, they were far more accustomed to fighting unconventionally which made them an especially deadly foe for the S'southi.
====Lights of Purity====
Having grown into a far more powerful faction on the Galactic stage following the Skull Campaign, the Lights of Purity was one of the many remnant factions that had become strong enough to pose an actual threat to the UNSC. When the S'southi invaded, the Lights of Purity formed a united front with other Covenant factions and lead them as a unified force alongside other members of the Galactic Alliance.
====Griccetus Covenant====
Following the Skull Campaign, Griccetus and his remnant faction had reconciled with the Lights of Purity and formed a loose alliance in order to protect eachother against growing external threats. Uncharacteristically for a brute, Griccetus lead his Covenant as a proper military, favouring in-depth and heavy-handed tactics and strategies over brute force.
====Praddeus Covenant====
Having been on the losing side of the Skull Campaign, the Praddeus Covenant had come out of the war weakened. Not demoralised by this defeat, Praddeus lead his remaining forces on a brutal war against the splinter factions that had risen in the wake of the destruction of the Skull Covenant and the Tornusion Covenant, and by 2560 had both regained almost all of it's former strength and become a highly feared and respected force on the regional stage. Like many other Brute-lead factions, Praddeus and his Covenant were ruthless, merciless and determined, making them particularly deadly to the S'southi. 
====Other====
As the war carried on, several other species and organisations joined the Galactic Alliance. Among them were the Unggoy, who acted similarly to their role in the Human-Covenant War, being used primarily as cannon fodder. The S'southi eventually, especially in the later years of the war, came to fear the Unggoy due to their seemingly infinite numbers.
===The Forefathers===
The Forefathers were a series of highly complex and incomprehensibly ancient Forerunner ancillae. Lead by Binding Enlightenment, they were worshiped as gods by the S'southi.
====S'southi====
The S'southi were a highly advanced species native to the Andromeda galaxy. Their armada consisted of extremely strong vessels in large numbers and their ground army consisted of trained-from-birth warriors and great biological machines that wielded ferocious power.