Today we'll talk about planets, dimensions, and expansions.
Okay, so bit of a timeline/lore question. As I understand it, we shut the original Dark Portal in WCII, right? And in doing so we trapped a sizeable force of Alliance (and Horde?) guys on the other side? Was this when Alleria and Turalyon ran through a portal? And did a Horde force run through that portal too?
Is there a good book to read up on this particular moment in Warcraft history?
And what were the Alliance/Horde forces doing while the DP was closed?
Alleria and Turalyon were part of a larger group known as the Alliance Expedition, which was sent out on a mission to get the Book of Medivh back from Ner'zhul and stop him from opening portals to worlds besides Azeroth. The group also included Khadgar, Danath Trollbane, Kurdran Wildhammer, and others. By the time they actually tracked down Ner'zhul he had already learned all he needed to know to lay siege to other worlds, so they made the tough decision to destroy the Draenor-side Dark Portal, sealing Draenor (now Outland) off from the rest of the universe. The remaining Horde forces either splintered into their old clans or joined up with Kargath Bladefist at Hellfire Citadel. The Alliance forces attempted to make some semblance of a life for themselves while enduring skirmishes with natives, with varying degrees of success.
You can read the complete story in the Beyond the Dark Portal novel.