While we've been off fighting Arthas and leaving a piece of ourselves in the cold northern wastes, Deathwing the Destroyer has been brooding in Deephome, the elemental plane of earth, for some time now. As he regained his strength and was patched back up by the denizens of the plane, he prepared for his assault on Azeroth. With cataclysmic force, he burst through the ceiling of the elemental plane and brought destruction to Azeroth.
Nearly all areas of Kalimdor and the Eastern Kingdoms were affected by the eruption. The Barrens is cleft in twain, with an enormous volcanic fissure splitting it into two different zones. Orgrimmar has been destroyed, prompting Garrosh Hellscream not only to rebguild the city, but to voraciously expand the Horde's territories. The Desolace shoreline was cracked open, allowing water -- and life -- back into the zone. Auberdine has been flooded and destroyed, forcing the Night Elves to move north. Everything and everyone is affected.
Deathwing's great Cataclysm had significant effects on not only Azeroth, but on the races that inhabit it -- especially some groups that might normally not seek help from other races.
The goblin home island of Kezan had an active volcano erupt under it, prompting a Trade Prince to cheat his fellow goblins into being sold into slavery while trying to escape the island. After their ship gets accidentally involved in the middle of an Alliance-Horde sea battle, the Goblins find themselves washed onto an island off the coast of Kalimdor -- fighting unknown enemies and joining unlikely, but familiar, allies.
Meanwhile, the reclusive residents of Gilneas, locked behind the Greymane Wall for a decade, have found themselves suddenly exposed for what they really are. Having summoned the ferocious Worgen race during the Third War to combat the Scourge, the Gilneans found themselves quickly overwhelmed by the creatures, and the curse that spawns them spread unchecked throughout the kingdom. Assaulted by the Forsaken, moving southward to claim the kingdom for themselves, the transformed Gilneans find themselves in need of two things -- a cure, and a hand. With the night elves promising to aid their lupine allies, the Worgen are welcomed into the Alliance.
Deathwing not only sundered Azeroth -- he also brought the Elemental Planes closer to Azeroth. In many places, the planes are pushing through to terrestrial Azeroth. Ragnaros the Firelord, lord of the elemental plane of fire, has been seething from his defeat at the hands of 40 adventurers and has brought forth his fiery wrath on Mount Hyjal. The Abyssal Maw, the elemental plane of water, has been raised along with the Lost City of Vashj'ir -- Lady Vashj's domain, and with it a strange yet-unseen sentient race. And Deepholm has been thrust through the planet's crust by Deathwing's eruption into the land of flesh.
The Cataclysm also has brought back forces previously absent in Kalimdor and the Eastern Kingdoms. Malfurion Stormrage has returned from the Emerald Dream to combat Ragnaros. The Titan stronghold of Uldum, long obscured from view by technology, has become visible since the machinery that shielded it was destroyed, and within it may contain a Titan superweapon -- or new allies. Grim Batol, Deathwing's former place of imprisonment, is now reopened in the Twilight Highlands east of the Wetlands, where he raises his new Twilight Flight.
Meanwhile, Horde and Alliance tensions rise. Garrosh Hellscream's temper rages unchecked through the Horde, and Thrall's ability to rein him in lessens with each passing day. As he pushes to expand the Horde's holdings on both continents, battles rage. The Forsaken march on Gilneas, the last remaining human kingdom in the Lordaeron region. With everyone having left a piece of themselves in Northrend, even a tenuous peace may no longer be possible.
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