A narrator discusses how survivors of the Third War never truly believed that the war had put an end to the Burning Legion. Just that Kil'jaeden was cut off from Azeroth but not indefinitely. Yet with the threat of war between Horde and Alliance, and continuing danger of the scourge, they could not prepare for a war that could happen millennia in the future, when danger was already happening around them.
With the portal newly opened, people had to reevaluate their priorities. Draenor had not been destroyed, but had become outland, where Illidan Stormrage is fighting to solidify his power base. Many of the loved ones they had thought perished with Draenor were still alive. Tracts of land were left untouched by fel magic or Ner'zhul's reckless sorcery. Recently, horde and alliance have gained new allies in the blood elves and draenei.
With the reactivation of the portal, it has become a double-edged sword. Illidan and his forces are fighting to keep all the other portals in Outland closed, but his loyalties remain in question. Should even one of the portals open, the forces of the Legion would invade Outland. Their inevitable triumph over Illidan would set off a chain reaction, with countless more worlds falling to the legion, Azeroth would have little hope.
To prevent such a scenario, the people of Azeroth have sent out scouts to bring back information from outland. They now understand the current layout and disposition of the enemies in Outland. They have compiled maps, bestiaries, and strategies. Knowledge that is key to the conquest of Outland.
Unfortunately tensions between Horde and Alliance remain, and they cannot be set aside lightly. The narrator thinks of the lives lost and grieves bitterly. He wishes to kill, but cannot afford to be blinded by bloodlust. He remembers that it was the Burning Legion that first set his people at one another's throats. He cannot permit the burning crusade to engulf other worlds. He must bring the war to an end, and find a way.