Before the Sunreavers, there was Aethas Sunreaver, Archmage of the Kirin Tor. Born of Silvermoon, survivor of the Scourge and Burning Legion assaults on Silvermoon and Dalaran, Aethas Sunreaver ushered in a new age of cooperation and worked to restore the alliance between Quel'Thalas and Dalaran, but in the end, he failed to preserve the neutrality of the Kirin Tor and saw himself and his followers either driven out of Dalaran or imprisoned in the Violet Hold ... the very same prison that the fallen Sindorei prince Kael'Thas once languished within, waiting for death at the hands of Garithos and his human soldiers.
Aethas Sunreaver has always had to walk a difficult line, and it has cost him dearly. It was Aethas who cast the deciding vote that led to Dalaran supporting Theramore as Garrosh Hellscream's forces marched against Jaina Proudmoore's city. It was also Aethas, alongside Rhonin, who suggested that Thalen Songweaver assist in the defense of Theramore, only for Thalen to betray the city to the Horde. After the destruction of Theramore and the death of Rhonin, Aethas even supported Jaina's rise to leadership of the Kirin Tor.
In the end, however, it made no difference. That narrow line Sunreaver sought to walk grew ever thinner, until finally it snapped. Now the Sunreavers are bereft of their home, and forced to rely on the very Horde that they were beginning to view skeptically. Here is how the group the Horde will fight for in Patch 5.2 came to be.
Aethas Sunreaver's origins are unknown -- we do not know his age, although it seems likely that he is a younger elf, one who embraced the change from High Elves to Blood Elves, and that he is Kael'thas Sunstrider's junior since he replaced the former prince in Dalaran. (Some argue that the reason we never seen Aethas' face is that he is Kael'thas, but there is no evidence of this.) Aethas took part in the migration of Dalaran to Northrend as a member of the Council of Six, the leading body of mages in Dalaran and its ruling council. As such, Aethas experienced firsthand the madness of Malygos and the dire urgency of the conflict called the Nexus War, and it was in support of Dalaran that he went hat in hand (so to speak) to Silvermoon to plead the case of the Council of Six to Lor'themar Theron and Grand Magister Rommath.
It didn't go well for Aethas. Rommath held the Kirin Tor in contempt for their role in allowing Kael'thas to be imprisoned in shattered Dalaran after the Burning Legion's assault, and for nearly allowing Garithos to execute the Blood Elves so imprisoned during the war against the Scourge. Nothing Aethas could do or say could appease the Grand Magister, who was not inclined to allow a single mage of Silvermoon to assist the Kirin Tor against Malygos. Indeed, it was only through the intervention of Sylvanas Windrunner that the Blood Elves agreed to take part in the conflict in Northrend, and even then it was primarily through Sylvanas' extorting said aid on penalty of loss of Horde support. This wasn't how Aethas wanted Quel'Thalas to come to Dalaran's aid -- he wanted the blood elves to renew the ancient alliances between the Kirin Tor and Quel'Thalas, to restore the thousand year bond between the two cities forged when humanity had come to the aid of the elves during the Troll Wars. It was the elves of Silvermoon who taught humans to use magic and thus created both the Kirin Tor and Dalaran, ultimately, and Aethas saw this ancient tradition as worth preserving.
Supplicant for the Kirin Tor
Furthermore, while loyal to his people, Aethas was dubious of the Horde. He served as their partisan during the discussion of how to fight the Nexus War, arguing successfully that Dalaran's position trapped between Malygos and the Lich King was too precarious to allow them to turn away any willing allies in the fight, and in so doing managed to create a 'Horde quarter' in the ancient city that the Old Horde had once besieged. Yet Aethas grew to distrust Garrosh Hellscream, and view his influence as suspect. After Malygos and the Lich King were dealt with, for a time Aethas could simply see to his duties as a member of the Kirin Tor, perhaps because both the Alliance and Horde were distracted by Deathwing's Cataclysm.
Following Deathwing's destruction, however, Aethas soon found the Kirin Tor swept up in the events that followed -- a Horde force seized the Focusing Iris, killing the members of the Blue Dragonflight sent to escort it to safety. Soon, Jaina Proudmoore came to Dalaran seeking help for her besieged island of Theramore, and despite misgivings about losing the modern neutrality he'd fought for, Aethas agreed that Garrosh's actions were unconscionable, and he voted to support the Kirin Tor attempt to dissuade the Horde via protective intervention. And in so doing, Aethas doomed his faction to exile and himself, too. How could he have known?
Keeper of the flame that burned him
Aethas suggested Thalen Songweaver for the mission, true, but so did Rhonin. Neither saw the man's treachery. After Rhonin's death Aethas vowed to make amends for what Thalen had done -- it was perhaps out of that spirit of conciliation and guilt that Aethas supported the appointment of Jaina Proudmoore to the leadership of the Council of Six, the position held by Rhonin and Jaina's teacher Antonidas before her.
However, it can also be attributed to a touch of vanity and arrogance that Aethas didn't see a problem with returning to Silvermoon and assisting Lor'themar and Rommath with research into mogu soul prisons, knowing this research would be used by the Horde war machine. During this, he was exposed to Sha energies and ranted about his distrust for Garrosh Hellscream, going so far as to compare service to Garrosh to the path of fallen prince Kael'thas. Before being freed from the Sha, Aethas even stated that the Sin'dorei should break free of the Horde and walk their own path. However, another mage, Fanlyr Silverthorn, would take this argument completely away from Aethas. A member of the Sunreavers working for Lor'themar, and through him for Garrosh Hellscream, Fanlyr ended up assisting in a plan to infiltrate Darnassus and steal the Divine Bell, and he used Sunreaver portals to and from Dalaran to accomplish the theft of the Bell. Jaina, already reeling from the destruction of Theramore and having already refused to break Kirin Tor neutrality to help the Alliance in its war in Pandaria, lost control of her considerable fury. And Aethas found himself squarely in her crosshairs.
Jaina returned to Dalaran and called Aethas out on the Sunreaver's actions. Aethas argued (perhaps even truthfully) that he had no idea that the theft had occurred. Yet in the end, despite his support for Jaina on two previous occasions, she could not be reasoned with (and Aethas himself grew irritated with her) and demonstrated that while Aethas was an archmage, she was at least by right of power demonstratably his superior. She captured him (with minimal difficulty) and Rhonin's widow Vereesa Windrunner began the purge of Sunreavers from Dalaran. It was brutal, uncompromising, and for any blood elves who remembered back to the Scourge invasion of Quel'Thalas and Garithos' use of the Violet Hold as a prison for blood elves, completely intolerable. Not only did it drive Lor'themar more firmly into the arms of the Horde, but after Rommath and a hero of the Horde rescured Aethas, it drove Aethas and his Sunreavers firmly into the service of the Regent-Lord of Silvermoon. Now Aethas finds himself directly serving the Horde in Pandaria at Lor'themar's behest.
Did Aethas know of the theft of the Divine Bell beforehand? It's possible he did, but it's just as possible no one told him anything -- before the recent events Rommath distrusted him as a seeming lackey of the Kirin Tor, and Lor'themar still smarted from Aethas' comments claiming that Garrosh would take Silvermoon down the same path as Kael'thas. But it doesn't matter now. Now the Sunreavers have no where else to go. Their home for generations has been lost. Their leader forced to work directly for the Horde, whether he likes it or not. In the end, the narrow line of neutrality thinned so that it snapped under the pressure, and Aethas Sunreaver finds himself at war with the organization he sat at the head of, against the woman he himself elevated to its leadership.
While you don't need to have played the previous Warcraft games to enjoy World of Warcraft, a little history goes a long way toward making the game a lot more fun. Dig into even more of the lore and history behind the World of Warcraft in WoW Insider's Guide to Warcraft Lore.