The human Mage Medivh, scion of a mortal human and one of the last guardians, comes under the influence of the dark Titan, Sargeras (although it is revealed that he was possessed). Mad with lust for power, he offers the world of Azeroth to the bloodthirsty Orcs in exchange for the Titan's powers and unwavering loyalty of the Orcish Horde.
The Orcs begin a very swift invasion of Azeroth but are, at first, beaten back and Medivh himself is slain, putting an end to his quest for power and domination. However, fortunes take a turn for the worse when the Orcs assassinate King Llane, sack Stormwind Keep (the capital of Azeroth), and drive the humans from Azeroth north into the Lordaeron subcontinent (setting the story for Warcraft II: Tides of Darkness)