War of Passage
It is currently the year 118ER (Era of Reprieve), as measured in every nation that bore witness to a cataclysm that ended 118 years ago. That cataclysm was precipitated by unrestrained experimentation with dark and dangerous magic by the elves- the dominant race of the world until the war. 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 who have access to the most restricted libraries of the world. The destruction this old one brought with it from the Shadowfell is still visible in the ruins of once great 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.
The war, and the apocalyptic damage it caused, are known as today as the War of Passage. Among humans it is a story passed down by word of mouth or by written histories. Among elves it is still a living, terrible memory, and a stark lesson about what happens when the thirst for dark knowledge runs unchecked.