The Sundering was the cataclysmic event that split Alara into the five Shards. It was caused by an unknown planeswalker who drained the plane of its mana, breaking it apart as a result.
Sources
- A Planeswalker's Guide to Alara
- Wizards of the Coast (July 25, 2008). "Planes of Existence: Alara". magicthegathering.com. Wizards of the Coast.