The Void Collapse

The official end to the Cavalieath Empire.  After years of rebellion by almost every city state, a large metamagical collapse happened in the North Kal'Broath (present day Valgriddean sea), over the Imperial Elves City of Cavaliea.  It is unknown why this collapse happened, but it not only inverted space and time into the astral sea taking the entire city and surrounding country side with it, but also polluted the surrounding area for leagues.
To this day very little grows there, unless it is unnatural in origin.  
The most excepted explanation by dwarven scholars is that the court of Imperial Elven Archmagisters was attempting to power a new anitech device, as large as a palace.  To what end may never be known, but if true the device either failed spectacularly, or as a few conspiracy minded folks believe, was sabotaged by its likely creators.