A prince, a lady, and a desert to roam
Upon their arrival on Outland (using a portal created in Dalaran to escape Garithos and his troops), Kael'thas and Vashj set to look for Illidan. Vashj had told Kael'thas that the creeping malaise he and his followers were enduring was withdrawal from the arcane energies they had so long used with abandon, energies that had been destroyed with the Sunwell when Arthas Menethil had used it to raise the necromancer Kel'Thuzad from the dead. Since the Sunwell was gone, if Kael'thas could find no substitute, his people would become increasingly ill as the addiction worsened. Vashj had told Kael'thas that her own people had suffered just such a withdrawal (as had his own, since they were at one time one people) after the destruction of the original Well of Eternity and that Illidan had an understanding of the situation, since he himself had been present during the events of the long-ago War of the Ancients.
By now more than just a little desperate, Kael'thas went along with Vashj. Stranded in an alien landscape of floating islands of rock and seared red soil, his blood elves and her naga searched for Illidan. They did not find him in the best circumstances.
Again in chains
Illidan for his part had fled Lordaeron following the confrontation with his brother Malfurion. He knew that in failing to use the Eye of Sargeras to destroy the Lich King, his patron Kil'jaeden would consider his life forfeit. Being somewhat attached to his life and desiring to hold onto it, he'd used the memories of Gul'dan in his head to consider a new place to retreat to: Gul'dan's former home of Draenor.
Sadly, Gul'dan's memories didn't include things that had happened after his death, like the fact that his former mentor had blown the whole place up. Illidan arrived on a world ripped into pieces and soon found himself hunted through this unfamiliar landscape by his former jailer Maiev and an army of her Watchers. This force ran him to ground and captured him.
In fact, they had just managed to secure him for transport when Vashj and Kael'thas finally tracked him down. After a running battle with Maiev's forces, Vashj and Kael managed to free Illidan from their hands. At first daunted when Illidan told Kael'thas there was no cure for the inherited addiction to magic wracking his people, the blood elf prince was willing to ally himself with Illidan when told that doing so would mean enough magical energy to sate the addiction and spare his people a slow death at its hands. With Kael's blood elves and Vashj's naga at his disposal and Maiev and her Watchers defeated and no longer a threat, Illidan was free to move on with his plans to secure Outland.
Against the demons
Illidan needed a place where he could hide from Kil'jaeden while consolidating his own power. Outland provided for both. As it no longer existed as a complete world in the Great Dark Beyond but was now a fragmented mass drifting in the Nether, it could only be accessed by powerful magics such as portals and vessels that could travel the dimensions, making it far easier to secure against the Legion. If you could seal the portals, you could effectively control your enemy's access to you far more readily than you could otherwise. Also, by having access to such portals, once you were in control, you yourself could scour all existence for powerful magical secrets.
Illidan saw in Outland the perfect first step in his campaign to not only escape the wrath of Kil'jaeden, but in time, to replace him. And why not? Illidan had gone from a mere night elf sorcerer to an entity powerful enough to kill a dreadlord with his bare hands; given enough time to accumulate power and knowledge, he could well found his own rival rorce of demons to oppose the Legion.
Kael'thas pointed out to his new master that the portals would need to be dealt with before Magtheridon. Any attempt to supplant the pit lord was doomed to failure. This led to a series of forays to seal up the portals before taking on the pit lord, and it was Kael'thas who saw a group of krokul, or broken, draenei under attack by orc forces loyal to Magtheridon. Possibly from compassion and possibly from his own inherently manipulative streak, Kael'thas helped the broken against the fel orcs and demons; in so doing, he brought Akama the elder sage and his broken into the service of Illidan.
Akama, formerly a defender of the Temple of Karabor who had mutated due to heavy exposure to fel energies (draenei, with their inherently magical natures, are extremely susceptible), found himself waging a guerrilla war against the numerically superior and magically powerful demons and their fel orc servants. With the world shattered by Ner'zhul and the demons ever increasing their numbers, Akama had very little hope of keeping his tribe intact or even alive, thus making an alliance with Illidan's forces the surest way to do both. While it would be a mistake to assume Akama was loyal to Illidan even then, he certainly preferred the former night elf to Magtheridon.
With this final piece of the puzzle, Illidan finally had the army he needed to wrest control of a world from the Burning Legion.
Illidan closed each portal, defended by his assembled forces. Bolstered by this successful campaign, the armies of the Betrayer marched on Magtheridon's stronghold in the Black Citadel (formerly the Temple of Karabor; as an aside, yes, the whole Black Citadel/Black Temple/Hellfire Citadel thing is messed up, but don't ask me to untangle it all here).
With the help of Akama's broken, who snuck into the temple and disabled its defenses, Illdan stormed the citadel itself and engaged first Magtheridon's fel orcs and demons, then the Pit Lord himself. In the end, cut off from his forces and used to waging straightforward battle against weaker foes that he easily crushed with his raw physical power, Magtheridon fell to the power of two of the greatest living mages and one of the best archers in existence.
Unable to comprehend his defeat, Magtheridon asked his conqueror if he had been sent by the Legion to replace him, a question Illidan mocked with triumphant laughter. Informing Magtheridon that he was in fact not sent to test him but rather had come to replace him, he had the pit lord sentenced to a fate worse than death. Imprisoned below the Hellfire Citadel, Magtheridon's blood would be used to create an army of fel orcs for Illidan's personal use.
Still, while Illidan's plan to conquer and hold Outland was successful, it had not escaped the notice of Kil'jaeden. It's debatable whether or not the manifestation of Kil'jaeden that appeared to Illidan following his defeat of Magtheridon was actually merely a vision or not, but one thing is certain: When confronted by Kil'jaeden, Illidan quickly lied through his teeth and claimed he had been amassing his forces for another attempt to destroy the Lich King. This blatant lie was so bald-faced that Kil'jaeden, despite all evidence to the contrary, accepted it. The new "Lord of Outland" would have another chance to destroy the Lich King. (I have to wonder if this was Gul'dan's influence at work, as it reminds me of when Gul'dan created death knights just to keep Orgrim Doomhammer from killing him.)
Next week, we see what had been transpiring in Lordaeron while all of this took place. Who would meet Illidan's forces in battle at the Frozen Throne? Why is a former high elf making an alliance with Garithos? Who rules the plaguelands? And who, exactly is the Traitor King?
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