The Doomsday Clock
The Veil is a mystical force that elves constructed to keep non-magical creatures from entering or leaving their land. While the elves did what they could to help the non-magical races during The Last War, they still did not trust them completely.
The Veil serves as a way to keep those non-magical races from the evils that could possibly have survived in the west and allow the elves the privacy they wish.
The Veil stars above The Kera Desert and extends northward across the sea to the Great North. Magical creatures may cross The Veil freely but non-magical creatures simply may not and are met with an invisible force.