The cataclysm in question in Ivalice occurs sometime between FFXII and FFT. I always assumed that this cataclysm is not the same as the Ajora-Execution one. Regardless, however, it was responsible for the extinction of multiple Ivalician races, and the destruction of the relatively advanced civilizations found in FFXII.
A new Tactics Ogre is in development. Tactics Ogre: the Wheel of Fortune. Where will Fate lead you? (Lost hope for Asagi: August 5th, 2010, 1:15 am.)
It is also possible that it was another Ajora-related cataclysm, since we know that Ajora can reincarnate, has reincarnated (into a man and into a woman at the very least) and that Ultima is the Esper responsible for reincarnations.
Not changing this sig until Square Enix reveals that codename FORTRESS is actually FINAL FANTASY XV. You read it first on GameFAQs.