The problem with Warcraft 2 is that its campaigns weren't an ongoing storyline like in Starcraft or Warcraft 3. Each one takes place in a different alternate reality. In the Orcish campaign for Tides of Darkness the Horde invades Lordaeron, destroys Stratholme, Stromguarde, Hillsbrad, Quel'thalas and eventually conquers the entire continent. In the Alliance campaign the humans destroy all of the Orcish settlements, drive them back into the ruins of the Kingdom of Azeroth and ultimately destroy the Great Portal.
I own the Battle.net edition of WC2, so the instruction manual does include a brief preface for the expansion. Essentially it sounds like what is defined as canon from Tides of Darkness is that the orcs destroyed everything except Lordaeron itself, but the Alliance also pushed them and destroyed the Great Portal, in the end capturing every clan except for the Bleeding Hollow, which later escaped into Draenor when Ner'Zhul reopened the Great Portal as the Dark Portal. Alterac still betrayed the Alliance and was destroyed, Gul'dan and Cho'gall still betrayed the Horde and were killed--but Gul'dan was never captured by the Alliance. It's all very confusing.
Then in Beyond the Dark Portal there is a similar setup with the two campaigns. Depending on which race you play, Ner'zhul or Khadgar capture the Spellbook of Medivh and Skull of Gul'dan (which is either in Deathwing's Lair or the hands of some Bonechewer orc), and either open rifts to new worlds, destroying Draenor, or seal the Dark Portal and close the rift between Azeroth and Draenor forever.
It's looking like the orcish campaign is almost totally canon in this one, since Draenor was destroyed by Ner'zhul trying to open portals and the fel orcs do seem well established in Draenor. There doesn't seem to be much of Khadgar's Expedition left in Outland, and since they apparently failed in their mission it makes me wonder why they get honored with statues in the entrance to Stormwind City. What is also odd is that in Outland the Laughing Skull clan appears to be alive and well, and buddy buddy with the rest of the Fel Horde in spite of their earlier betrayal.
I'm gonna have to reread the intro in the instruction manual for WC3 to help get things straight.
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