cataclysm

The mad dragon deathwing is destroying the world and it's up to the heroes to defeat him

It started out when the old god n'zoth corrupted the black dragonflights aspect, neltharion the earth warder. Once this process was complete, neltharion turned into deathwing, the harbinger of the hour of twilight.  The old gods' victory of taking over azeroth. Content on destroying azeroth, the orc shaman thrall allied himself with heroes of the alliance and horde, as well as the remaining dragon aspects. When deathwing broke out of the earthren realm of deepholm, a swirling mass of land erupted out of the ocean. Now known as the maelstrom, doorway to deepholm. It was here that deathwing escaped the realm of deepholm, and it was here that he was destroyed, after sundering the world apart in a great cataclysm, the united aspects along with thrall and the heroes of azeroth destroyed neltharion, or at least all that was left of him.