The Great Cataclysm

Most people don't know a lot about the great cataclysm, even the gods with their immortality speak little of the event. It is known the cataclysm broke a once single massive continent into what is seen across the world today, all but eradicating the ancient and powerful races that called Discordia home before its impact. Old stories say those ancient races used their power to protect the world from the devastation, so that at least some remnant could remain. Dragonborn and Goliaths both have histories that say that some of the dragons and giants lived through the event, and briefly lead their ancestral races to safety, but then quickly disappeared never to be seen again. The large concentration of magic and unique resources that can't be found anywhere else in Discordia seem to support these histories.
Studying the Mountains of Kord have shown that there a great cave system underneath, but expeditions into the caves have either not been fruitful in their search, or have not come back at all, so the mysteries of this event and it true effects may never be known.Inside the caves of the Mountains of Kord a carved history of before the cataclysm is said to exist, explaining the cataclysm, the results of the destruction, and a path back to unifying the people of Discordia and bringing back the ancient races.
The seeming seperation of all the races also lends itself to what little as known, as sharing secrets and histories between races is generally frowned upon, in case in later gives them an advantage in finding items of power, or brings favor or retribution from their god.

Localization

The greatest physical remains of the great cataclysm can be seen in the Mountains of Kord, where the impact raised massive mountains that are all but impassable and have isolated the small groups that have made the impact site their home.