Alliance: Karabor, Shadowmoon Valley In the aftermath of the Dark Portal strike, Alliance players will be led to the pre-Black Temple, otherwise known as Karabor in search of allies to face the Iron Horde. Once there, you and other travelers will work together to save the draenei holy temple and turn it into a capital city for your faction. Stay alert though, while the Iron Horde lays siege to the temple, Ner’zhul and his nefarious Shadowmoon Orc clan pursue another line of attack that could put the entire world in mortal danger.
Horde: Bladespire Fortress, Frostfire Ridge Following the assault on the Dark Portal, Horde players will be led to Frostfire Ridge and the aid of the Frostwolf Clan. Once there, you will battle the ogres of Bladespire Fortress to secure a new base of operations in this harsh land. Don’t be fooled by your progress, though—the Thunderlord Clan will be right on their heels to reclaim their lands.
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Official Overview via Wowpedia 