What is the Dark Horde in World of Warcraft

The Dark Horde are a collection of Trolls, Ogres, Orcs and similar beings who have joined under the command of Rend Blackhand. Rend Blackhand claimed the title of Warchief, and does not consider Thrall the true leader of the Horde, having retreated into Blackrock Spire with his master, Nefarian.