Great War

The Great War was a destructive conflict fought between the protoss and zerg, ancient enemies both created by a progenitor race, the xel'naga, with several factions of terrans being caught in between.

Protoss
The protoss, a race of powerful humanoids united by a psychic link, were modified by their progenitors the xel'naga, millennia ago. The xel'naga considered the protoss to have purity of form. The protoss first worshiped the xel'naga as gods. The protoss started to lose their psychic link, and when the xel'naga abandoned them, the protoss fought a long civil war called the Aeon of Strife.

At the end of the war they regained the use of their link, which they called the Khala, and built a religion and philosophy around it. They believed straying from the link could provoke another civil war. However, a rogue group of protoss refused to join, and were eventually expelled by the protoss leadership, the Conclave.

Approximately 2300, the terran colonists arrived in the Koprulu Sector, in the shadow of protoss space. Under the dictates of the Dae'Uhl, the protoss philosophy concerning other species, the protoss secretly watched them from afar.

The protosss, constantly on the lookout for xenomorphic threats, intervened in terran affairs when the Koprulu Expeditionary Force under the command of Executor Tassadar discovered zerg probes near terran worlds.

Zerg
The zerg were a species of parasitic worms which evolved on the ash world of Zerus near the galactic center. The xel'naga discovered them and, considering them to have purity of essence, pushed their evolution. In order to keep the zerg from losing this purity, they created the Overmind, their collected sentience.

The zerg had the ability to absorb genetic material from other species, consuming what they wished and leaving behind the rest. Soon they had taken over the planet. The Overmind became aware of the xel'naga and, after absorbing a space-faring species, threw the Swarm at the xel'naga worldships in orbit above this. The xel'naga fell, and the Overmind absorbed many of them into itself, learning many of their secrets, including the existence of a previously-modified species&mdash;the protoss. The Overmind immediately began searching for them.

While it absorbed numerous species on the journey, it feared the protoss' psychic abilities, and sought a species with psionic powers which it could absorb for itself. Approximately 2449, it discovered this species&mdash;humanity.

Terrans
The terrans were discovered by the zerg approximately sixty years before the Great War. However, the Terran Confederacy only discovered the zerg almost five decades later. They went to great lengths to destroy the initial infestation, which was found on multiple fringe worlds, but kept a number of the xenomorphs for study. By 2491 they were using psychics in experiments with the creatures. These experiments became known to Arcturus Mengsk, leader of the Sons of Korhal, after he stumbled upon them while pursuing his insurgency against the Confederacy.

Prelude

 * Main article: Battle of Chau Sara

By 2499 the zerg Overmind had reached the Terran Confederacy colony of Chau Sara. It seeded the atmosphere with spores, subtly infesting the soil.

The zerg also invaded other Confederate colony worlds, such as nearby Mar Sara, as well as Brontes and Dylar IV.

In November, the Terran Confederacy lost control of one of its experiments on the zerg at the Flannum Installation on Chau Sara.

The Confederate forces eventually defeated the zerg, beating them back from the capital, Los Andares. The Confederacy controlled all communication and travel to the planet, hiding the events of the battles.

The Zerg Swarm took over Chau Sara, but by next month, Tassadar's Koprulu Expeditionary Force arrived there. The Conclave ordered the fleet to begin a purification operation against the planet. The Overmind ordered its forces to hold back so it could observe the operation. All life on the surface of the planet was extinguished.

Confederate colonel Edmund Duke, fearing an attack against the nearby colony of Mar Sara, launched a clumsy counterattack against the protoss fleet. Tassadar retreated out of respect for the terrans' bravery.

The panic generated by the news inflicted an economic slowdown on the Confederacy, which it had been enjoying since their victory in the Guild Wars.

Battles of Mar Sara
The Terran Confederacy extensively manipulated the media at Mar Sara and abroad while instituting a policy of forcible and deliberate neglect on the citizenry of Mar Sara. Even the colonial magistrate was forced to relocate as the Confederate military effectively overthrew the local government. Colonists were moved to concentration points in the wastelands.

Hostilities broke out between the Confederacy and the Sons of Korhal. The Mar Sara Colonial Militia fended off an attack against one of their command centers, then destroyed the nearby rebel base.

Loss of Support
A team of Confederate marines, firebats and SCVs at Backwater Station fell under attack from the zerg. Colonial marshal Jim Raynor offered to help rescue them, but Edmund Duke ordered him to stay away. Raynor insisted on taking his forces to the rescue anyway. During the battle, the terran combatants discovered an infested command center and destroyed it. Reports about the battle from Universe News Network reporter Michael Liberty prompted the Confederate military to arrest Raynor's militia branch, imprisoning them in a prison ship in orbit.

Fall of Mar Sara

 * Main article: Battle of Mar Sara City

Confederate policy would cost them the support of the magistrate of Mar Sara. His adjutant gave him a report showing the Confederacy avoiding combat with the zerg. The only source of military relief were the Sons of Korhal.


 * Main article: The Battle of Oasis

Meanwhile, the Confederacy planned to evacuate the planet, but had final operations to attend to. The Sons of Korhal had stolen a secret psi emitter from them, which lured zerg to its location in Oasis Station. The zerg had already taken the city. The 417th Confederate Marine Platoon was ordered to retrieve the item, but wasn't told of its properties. The platoon succeeded, capturing the box and a rebel operator, but were forced to flee to their base at Bunker Complex 3847, aka "Scenic". During the retreat they lost half the platoon, and the Confederacy attempted to kill them (and destroy the box) by dropping a tactical nuke on them. However, the attempt failed, leaving the platoon initially unaware they had been targeted for death. They took shelter in the mysteriously abandoned bunker complex.


 * Main article: The Battle of Scenic

Arcturus Mengsk and his new ally Michael Liberty embarked on a strategy to gain the colonists' support. He promised to rescue them from the zerg, which the Confederacy was conspicuously failing to do, even though his dropships were unlikely to reach Mar Sara City in time; they were five hours away.

The rebel operative informed the platoon of the emitter's properties, and they became aware of the situation at Mar Sara City. By activating the device, they could lure flying zerg to their location rather than the city, delaying the zerg long enough to allow its evacuation. They activated the device and transformed the bunker complex into a defensive-oriented death trap during the hour-and-a-half they had before the zerg arrived. Then they fought a battle to the death, delaying the zerg as long as they could&mdash;enough time for the dropships to reach Mar Sara City&mdash;before being completely wiped out.


 * Main article: The Siege of Mar Sara City

Mengsk struck an alliance with the magistrate. His militia had to hold out against the zerg for half and hour until the Sons of Korhal dropships could arrive. Due to the delays imposed by the 417th Confederate Marine Platoon on the zerg, the militia was successful in keeping the zerg away from the civilians until they could be evacuated.

Meanwhile, the Sons of Korhal rescued Jim Raynor from the prison ship, inducting him into their organization.


 * Main article: Raid on the Jacobs Installation

The Sons of Korhal planned their own evacuation of the planet, but not before stealing weapons designs from the Confederacy. Jim Raynor was selected to lead a team of marines and firebats into the Jacobs Installation. The team fought their way inside, killing Alpha Squadron soldiers and even captive zerg and retrieved a data disk, but this prompted the installation's self-destruct sequence. The team escaped shortly before the structure exploded.

The Sons of Korhal fled to the colony world of Antiga Prime. Thirteen hours later, the protoss purified Mar Sara.