Shattrath and WoW History and Lore

When the Burning Legion turned the orcs against the draenei, the fiercest battle was fought [in Shattrath]. The draenei fought tooth and nail, but in the end the city fell. The city was left in ruins and darkness...until the Sha'tar arrived. The Sha'tar, or "born from light" are the naaru that came to Outland to fight the demons of the Burning Legion. They were drawn to the ruins of Shattrath City where a small remnant of the draenei priesthood conducted its rites inside a ruined temple. [...]

The priesthood, known as the Aldor, quickly regained its strength as word spread that the naaru had returned and reconstruction soon began. The ruined temple is now used as an infirmary for injured refugees. It wouldn't be long, however, before the city came under attack once again. This time, the attack came from Illidan's armies. A large regiment of blood elves had been sent by Illidan's ally, Kael'thas Sunstriders, to lay waste to the city. As the regiment of blood elves crossed [the] bridge, the Aldor's exarchs and vindicators lined up to defend the Terrace of Light.

But then the unexpected happened. The blood elves laid down their weapons in front of the city's defenders; their leader Voren'thal stormed into the Terrace of Light and demanded to speak to A'dal. As the naaru approached him, Voren'thal kneeled before him and uttered the following words: "I've seen you in a vision, naaru. My race's only hope for survival lies with you. My followers and I are here to serve you." The defection of Voren'thal and his followers was the largest loss ever incurred by Kael's forces. And these weren't just any blood elves. Many of the best and brightest among Kael's scholars and magisters had been swayed by Voren'thal's influence. The naaru accepted the defectors, who would be known as the Scryers.

The Aldor are followers of the light and forgiveness and redemption are values they understand. However, they found [it] hard to forget the deeds of the blood elves while under Kael's command. Many of the priesthood had been slain by the same magisters who now vowed to serve the naaru. They were not happy to share the city with former enemies. [..] The attacks against Shattrath continued, but the city did not fall, as you can see. On the contrary, the naaru known as Xi'ri led a successful incursion into Shadowmoon Valley - Illidan's doorstep. There he continues to wage war on Illidan with the assistance of the Aldor and the Scryers. The two factions have not given up on their old feuds, though. Such is the animosity that they vie for the honor of being sent to assist the naaru there. Each day, that decision is made here by A'dal. The armies gather here to receive A'dal's blessing before heading to Shadowmoon.

The city now serves as the headquarters of the naaru and has areas set aside for the Scryers and Aldor factions.