Aeon of Strife

The Aeon of Strife was a massive civil war amongst the protoss, even earning the status of the "bloodiest, most violent civil war ever recorded in galactic history".

Background
The protoss were a race of humanoid hunters with psychic powers which developed on the world of Aiur.

They were discovered by the xel'naga, a powerful and ancient race, looking to extend their own lifespan by locating a species with purity of form.

The xel'naga became intrigued by the mental link which all protoss shared. From above, they manipulated protoss evolution. After some time, they descended to the surface and lived with the protoss, who worshiped them as gods. The protoss Shelak Tribe shared the closest bond with the xel'naga.

Prelude
Protoss science and psionics advanced at a fast rate, but so did their pride and egos, causing the tribes to drift apart. The protoss began to shy from their xel'naga teachers as they grew suspicious of their interests and cultivated unsubstantiated rumors about them. The tribes began to lose the connection to their psychic link.

The xel'naga, saddened at the lost opportunity, made ready to leave Aiur. Seeing this as a betrayal, some protoss attacked them, killing many hundreds of them, even attacking their ships as they left.

The xel'naga abandoned many artifacts, including an underground city and khaydarin crystals. The Shelak Tribe safeguarded many more portable artifacts.

The protoss then fell into a state of madness in which they raged and whimpered. Each protoss felt great self-hatred over their abandonment by the xel'naga, and the madness was a symptom of this. The tribes held a love/hate relationship with the xel'naga and felt great hatred toward other tribes.

History
During the Strife, protoss advancement slowed, and the individual protoss tribes waged a massive war with each other. Little is known from this time due to loss of historical records. The most famous tribe from this time period is the Akilae Tribe, which are to this day renowned as the protoss' finest psionic warriors.

During this time, the protoss maintained colonies on other planets, often connected by warp gates, but these too quickly became gripped with the Strife.

The protoss tribes descended into something resembling madness as they attacked one another. One example was the Mendella Incident, where the mainly underground settlement of Mendella was flooded when another protoss faction deliberately destroyed a nearby reservoir.

As the Strife drew on, many tribes focused their attacks on the Shelak Tribe, as they had been closest to the xel'naga.

He Who Brings Order
During the latter part of the Strife, the Shelak Tribe was frequently attacked by other tribes due to their constant veneration of the xel'naga. These attacks sometimes focused on the artifacts rather than just the tribe members.

Savassan and his apprentice Temlaa were scholars, more interested in studying the artifacts than in engaging in war with the other tribes. They announced they would leave the tribe in order to better study them. The two began to decipher the copies of the writing on the artifacts.

During their journeys, they happened upon a trove of khaydarin crystals and were able to form a psychic link with each other. When they returned to the tribe to show off their discovery, however, Telkar, the Shelak Tribe leader, insisted on using the crystals and techniques as a weapon. Savassan believed that mentally linking with other tribes would instead end the war, since the protoss would realize what things they had in common (such as love of family, desire to defend their tribes, etc).

Further deciphering of the relics led the two scholar to the underground city. There they discovered what sorts of experiments the xel'naga had conducted on the protoss, including a giant khaydarin crystal which drained protoss of their life energies. While Temlaa was frightened, Savassan noted the xel'naga had experimented on all tribes and treated them equally. Savassan subjected himself to the crystal's draining for a limited time before Temlaa rescued him. From the crystal, Savassan learned much about the xel'naga.

Savassan learned the way which protoss society could be healed. The loss of the species-wide psionic link caused the self-hatred that drove the Strife, of which their schizophrenic love/hate toward the xel'naga was merely a symptom. Re-creating the link would enable the protoss to heal by feeling the collected positive emotions and end the Strife.

With this power, Savassan, now known as Khas ("He Who Brings Order") traveled through Aiur, teaching the protoss he encountered to join the psionic link; this became a philosophy called the Khala. He demonstrated the powers of the khaydarin crystals at Gyras, where he ended the feuding by destroying the battleground. Eventually Khas reunited the majority of the protoss, forming three castes and a new tribe.

The very first group of warriors and students to surround him became the Ara Tribe, and joined the Judicator Caste. The other tribes who quickly joined also became members of this caste.

The next group of tribes became the Templar Caste (the warriors), and the majority of the protoss became the Khalai Caste (workers and artisans), ending the civil war. The theory known as the Khala brought on the Second Age for the protoss.

During this period in protoss history, the Templar Caste fought to protect the new protoss culture from those who disagreed with it.