It is called The Great Knock. A giant Hand from the clouds reaching down smashing or grabbing at various places around the world. Civilizations ceased to exist in moments. Seas drained, mountains crumbled. Some have said the gods were angry with the people, others have said that the gods were angry with themselves. Others say the gods had nothing to do with it. That it was demons who tried to destroy the earth and the gods only became involved to drive the demons off the Prime Plane.
That was 1500 years ago. The survivors began the slow process of rebuilding… The Forgotten Realms.
“the stars have aligned, pray the Hand does not return”