The Dim Wastes
It is currently the year 3231ER (Era of Reprieve), as measured in every nation that bore witness to a cataclysm that ended 3,231 years ago. That cataclysm was precipitated by unrestrained experimentation with dark and dangerous magic by the elves- then the dominant race of the world. In their fervor to discover ever greater power, they weakened the fabric between the Material Plane and the Shadowfell, and drew the attention of an unimaginably powerful entity native to that dark place.
The name of that vile thing is now known to only a few, with access to the most restricted libraries of the world. The destruction this old god brought with it from the Shadowfell is still visible in the ruins of great elven cities scattered across the continents. The war it ignited saw the first, (and only) unification of elves, men and orcs under one banner. In the end, the enemy was defeated and banished back to the Shadowfell, but the cost was great. It’s parting shot was a curse carried upon the very wind, rendering all elvenkind unable to bear children, and dooming the race. The race of elves withdrew somewhat from society at large, focusing their efforts on finding a way to lift the curse over their race. In time, they vanished completely and human rose to become the most populous of the intelligent races.
The war, and the apocalyptic damage it caused, are known as today as the War of Passage. Although the last of the elves vanished from society well over 1000 years ago, half-elves still walk among men, though they are few in number. Whatever the explanation, elven blood seems to see its own way through generations, once introduced.