The Great War, also sometimes called the First War in some regions of space, was a massive military conflict between the zerg, the protoss, and the humans of the Koprulu Sector. The events of the war were predicted eons earlier by the xel'naga, who had also created the protoss and the zerg.
Prelude[]
The Terran Confederacy first discovered the zerg as deep-space probes. Unbeknownst to the humans, these probes were sent ahead of the larger zerg swarm by the Overmind. The Terran Confederacy also learned that they could lure zerg to planets using the psi emitters they had initially created to enhance the psionic capabilities of Ghosts. Hoping to eradicate their rivals while managing to be declared heroes, the Confederacy began experimenting in the hopes of turning the zerg into a bio-weapon of sorts.
Meanwhile, the entire zerg swarm arrived in the Koprulu Sector. They infiltrated colonized worlds, infecting the atmosphere with spores that allowed the creep to grow so that the zerg could develop small hive clusters.
The protoss purify Chau Sara
Then, the Terran Confederacy lost control of the zerg at Flannum Installation on Chau Sara. They battled against the aliens, almost defeating them at Los Andares. The zerg retaliated by overrunning the planet. The protoss' Koprulu Expeditionary Force, led by Tassadar, arrived and purified the planet -- eradicating all life on its surface. The Conclave ordered that any planet with any possibility of infection by the zerg be treated the same genocidal way. Tassadar, however, sought to find a way to combat the zerg threat without destroying human life.
The War[]
Edmund Duke, a colonel of the Terran Confederacy, launched an attack against the Protoss fleet. Impressed by the bravery of the humans, Tassadar withdrew his forces to the edge of the Koprulu Sector. Unfortunately this -- combined with Tassadar's reluctance to commit genocide -- allowed the zerg infestation on Mar Sara to fester.
Battles of Mar Sara[]
As it became clear to the Old Families that Mar Sara, unbeknownst to its magistrate, would be caught up in the brewing war between the protoss and the zerg, the colonists living there were forcibly relocated to the Wastelands. These would be, they were told, an easier place for them to be evacuated from the planet. Instead, the colonists were left to their own defense. When the Mar Sara Colonial Militia, led by Marshall Jim Raynor, discovered an infested command center and destroyed it Edmund Duke had them declared criminals for destruction of Confederacy property. Raynor and his militia cohorts were arrested and imprisoned on a prison ship in Mar Sara's orbit.
This betrayal cost the Confederacy the loyalty of the magistrate, who threw his lot in with the Sons of Korhal. Meanwhile, the Confederacy made a concerted effort to destroy any evidence of the psi emitter that had been on Mar Sara -- a device which had fallen into the hands of the Sons of Korhal. The 417th Confederate Marine Platoon was sent to retrieve the device -- a mission which pitted them against both the zerg and the Sons of Korhal. During their escape, the Confederacy targeted the marines with a nuke -- an attempt which failed, leaving the platoon unaware of their near-death at the hands of their own government.
Using the psi emitter, those left on Mar Sara were able to lure the zerg to Mara Sara City and buy time for those who needed to be evacuated. The Arcturus Mengsk and the Sons of Korhal arrived to the planet with dropships just in time to save those left alive on the surface. They also freed Raynor and his militia -- now calling themselves Raynor's Raiders -- from the prison ship and inducted them into the organization. During the evacuation, Raynor's Raiders infiltrated the Jacobs Installation to steal weapons schematics from the Confederacy. The Sons of Korhal and those they had rescued fled Mar Sara for Antiga Prime -- and thirteen hours later, the protoss purified Mar Sara.
Antiga Prime[]
The Sons of Korhal established a base for themselves on the second moon of Antiga Prime, eager to use that as a staging ground for a colonial revolt. Jim Raynor and Sarah Kerrigan led an effort to destroy the zerg presence in the area -- which succeeded and also destroyed a Confederacy base. This threw the Confederates into a panic and during the chaos, the Confederate flagship Norad II crashed.
The vessel began to be assaulted by the zerg, forcing Edmud Duke -- who was aboard -- to send out a distress signal to any who might be able to lend assistance. Arcturus Mengsk saw an opportunity, and sent Raynor to save the survivors. As a result, the Confederacy's Alpha Squadron became loyal members of the Sons of Korhal. The Confederacy created a blockade around Antiga Prime.
Meanwhile, the Fist of Redemption -- who saw the zerg as the salvation of mankind -- traveled to Brontes IV and attempted to aid the zerg infestation there. The Council of Inquiry, the government of the planet, saw fit to create the Hammer Strike Force to combat the threat. The Terran Confederacy sent a number of Ghosts to assist. The protoss arrived, but decided to attempt to salvage human life by simply fighting the zerg on the planet. Ultimately, this method failed and the planet was soon totally overrun.
Things began to fall into a predictable pattern -- the Sons of Korhal would inspire a rebellion, the Terran Confederacy would tighten its grip, the humans would fight amongst themselves and then be helpless against a zerg invasion. The protoss would destroy all life on the planet.
Antiga Prime is purified
Finally, Antiga Prime became the focal point once more. Delta Squadron attacked the Sons of Korhal, prompting them to construct a psi emitter. Kerrigan infiltrated the Confederate base and activated the emitter -- drawing zerg from light years away. The Confederate blockade stood its ground, which allowed the Sons of Korhal to escape. Raynor rescued what colonists he could, beforethe protoss arrived and purified the planet.
Fall of the Confederacy[]
The war waged on, and eventually Mengsk chose to invade Tarsonis. The orbital defenses were considerable, but Edmund Duke knew his way past them. Leading his Alpha Squadron from Norad II, they fought their way past Delta and Omega Squadrons and cleared the path to the planet. Fighting descended to the planet's surface, and into Tarsonis City. Psi emitters were activated on the planet.
The psi emitters drew the zerg to Tarsonis, but the protoss followed almost immediately behind them. Mengsk feared interference from the protoss would allow Confederates to escape, so he ordered Kerrigan to defend the hive clusters at New Gettysburg. The battle turned into a heavy, bloody four-way conflict. The zerg eventually overran the other combatants, and Kerrigan was abandoned despite pleas for support. Raynor and several others were horrified.
Mengsk ordered his forces to withdraw from Tarsonis, but Raynor and his allies defied orders to rescue any survivors. Despite their best efforts, they could not find and rescue Kerrigan. The Confederate Resistance Forces also escaped Tarsonis at this time, and regrouped elsewhere. The zerg, meanwhile, remained on the planet for some time before relocating themselves to Char.
Arcturus Mengsk, having defeated the Confederacy, declared himself the head of the new human government of the Koprulu Sector -- the Terran Dominion. The Dominion battled the zerg, withholding aid from any planetary government that would not swear allegiance to them -- claiming that each planet's invasion was their own internal matter. Soon all of the human governments of the sector were united under the Dominion. Meanwhile, Raynor and his Raiders were making an effort to get as far from Mengsk as possible.
Rise of the Queen of Blades[]
Psychic emanations from the planet Char led Mengsk to send Edmund Duke to the planet. He was routed by the zerg, fiercely defending a growing chrysalis. Raynor's Raiders arrived soon afterwards -- in time to witness what emerged from the chrysalis. It was a new Sarah Kerrigan, dubbing herself the Queen of Blades. She permitted the heavily damaged Raiders to escape alive.
Kerrigan led the zerg to acquire more information on the Ghost Program, so that she might unlock the true potential of her psionic capabilities.
Meanwhile, Raynor met the Dark Templar known as Zeratul and formed an alliance. Zeratul had slain the cerebrate Zasz -- causing the zerg to panic as they were forced to eliminate the out-of-control Garm Brood. Unfortunately, Zeratul had made psychic contact with the Overmind during the assassination -- and the Overmind had learned both the location of Aiur and how to physically manifest itself on that world. The zerg swarms traveled there with haste, leaving a contingency led by Kerrigan on Char to do battle against the alliance forming between Tassadar, Raynor, and Zeratul.
Aldaris and Artanis took command of the defense of Aiur. First, they led a battle to free Antioch from the zerg and rescue Fenix. Shortly after this, Tassadar managed to psychically pass a message to the Vanguard of Aiur, telling them about the cerebrates and that Zeratul had managed to kill one. Although Aldaris was shocked to learn that Tassadar had betrayed the Conclave by allying himself with the Dark Templar, Fenix boldly set out to destroy a cerebrate. He succeeded -- but the creature reincarnated before their eyes.
Hunt for Tassadar[]
Leaving Fenix to defend Antioch, Aldaris led an effort to destroy the hive clusters at Scion. Though Aldaris' efforts were successful, Fenix was defeated and presumed to be killed. Despite this, the tides seemed to be turning in favor of the protoss so Aldaris made it his mission to apprehend Tassadar and make him face the consequences for his betrayal. Aldaris dispatched a force to Char to complete this task.
On Char, the unlikely alliance between Tassadar, Zeratul and Raynor proved quite effective. They learned of a still active psychic-connection between Raynor and Kerrigan, which they exploited to lead her into a trap. Tassadar, wielding Dark Templar energies, slew Kerrigan's cerebrate -- causing her to lose control of her brood. She was able to regain a modicum of control before being confronted by the three leaders of the alliance. She quickly removed Raynor from the fight altogether, and then easily defeated the two protoss. The duel was interrupted by the arrival of Aldaris' forces. In the confusion, Zeratul vanished.
Tassadar, initially believing he had been sent reinforcements, was surprised to learn he was being arrested. He managed to convince the executor Artanis that Zeratul and the Dark Templar were vital to defeating the zerg. The two joined forces and began to search for Zeratul. They eventually found him, and convinced him to help save Aiur.
Protoss Civil War[]
When Tassadar and the Dark Templar arrived on Aiur, a civil war erupted in protoss society. The followers of the Conclave attacked -- forcing Tassadar and his rebels to defend themselves. Eventually, they launched their own attack on the Heart of the Conclave -- during which many members of the Conclave were killed. Heartbroken at seeing his own people killing each other, Tassadar turned himself in and was placed in stasis to await trial.
After Tassadar's surrender, Zeratul and his Dark Templar vanished. This left the reconstructed Fenix in command of the rebels. Fortunately, it was about this time that Jim Raynor, in command of the Hyperion, arrived at Aiur. The two mounted a combined assault to free Tassadar, which proved successful. Aldaris then attempted to stop the rescue mission, only to be attacked by the Dark Templar.
Fall of the Overmind[]
Realizing that the in-fighting between the protoss only served to aid the Overmind, Zeratul and his allies abandoned the battle and attacked a number of zerg cerebrates instead. Defeating the cerebrates was enough to weaken the zerg defenses, and clear a path to the Overmind. Joined by Raynor's Raiders, the Dark Templar and the protoss rebels engaged in one last stand against the zerg.
Death of the Overmind
Before the Overmind fell, the survivors of the Conclave saw the error of their ways -- though they did not participate in the climactic battle. The combined human and protoss forces overwhelmed the zerg, weakening the Overmind. However, the zerg inflicted plenty of damage of their own. In order to finally stop the zerg, Tassadar determined a costly path to victory. He channeled the Dark Templar energies through his ship the Grantrithor and crashed the vessel into the Overmind -- sacrificing himself but killing the Overmind in the process.
Aftermath[]
The remaining zerg ran rampant across Aiur, decimating the planet. The protoss were forced to abandon their homeworld. The zerg eventually came to be split into two factions -- those ruled by Kerrigan and those ruled by the cerebrate Daggoth. This division would ultimately lead to the Brood War.
Source[]
The Great War is derived from Starcraft.