Great Sundering

The catastrophic disruption of magic on Arn in the Second Age, resulting from the release of the Dwimmerwash during the Aqaa-dûr-Átalan. Cullereon became bereft of arcane magic and Cámyliarde became saturated with it.
On Cullereon, even the elves suddenly found themselves unable to tap into the arcane wellspring. Only the Sindaeri, who dwelt deep underground between the two sides of the world, were able to remain adept at both magic and warcraft.