World of Warcraft: Cataclysm is the third expansion set for the massively multiplayer online role-playing game (MMORPG) World of Warcraft, following the last expansion Wrath of the Lich King.
The central plot of the expansion is the return of the evil dragon aspect Deathwing the Destroyer. Last seen in Warcraft II, Deathwing has spent that time healing himself, and plotting his fiery return from the elemental plane of Deepholm. His return tears through the dimensional barrier within Azeroth, causing a sweeping cataclysm that reshapes much of the world's surface. In the midst of the world-wide disaster comes renewed conflict between the Alliance and the Horde, which is now under the rule of the warrior Garrosh Hellscream.
In the wake of Deathwing's rise, Azeroth has been transformed: previously lush jungle areas have been reduced to burning waste, while once-desert environments have undergone a similar-but-inverse change into fresh green growth. Likewise, the Alliance has pushed into the Barrens and destroyed Camp Taurajo, while the Barrens itself has been split in two by a massive volcanic fissure.
Source: Wikipedia, "World of Warcraft: Cataclysm", available under the CC-BY-SA License.