This is the official cinematic trailer for World of Warcraft's third expansion, Cataclysm. The original description for the content featured in this expansion is below. The full overview can be found here:
Without warning, the corrupted Dragon Aspect, Deathwing, erupts from the stone heart of Deepholm, the domain of earth within the Elemental Plane. Jagged fissures are torn across the earth, and monstrous waves pummel coastal regions. From Thousand Needles to the Blasted Lands, the surface of Azeroth is reforged through violent upheavals. Now, the Horde and the Alliance must defend their homes against Deathwing and his minions, burdened by the unsettling fact that the world as they know it has changed... forever.