Invisible Fortress:Balorian Crusade

The Balorian Crusade was a war waged by the fey against the population of all of Creation.

Prince Balor of the Terrible Gaze was helped by the Great Contagion that had been rocking the world for a few years prior to his invasion. Around 90% of the world's population had already died when the troops of the Feywild began their advance.

The reality-destabilizing nature of the fey massed in great numbers ate away at the borders of Creation, and the world today is notably smaller than it was before the Crusade. Ironically, however, that same destabilizing force disrupted the Great Contagion and prevented it from consuming the lives of absolutely everyone.

That respite from disease also spelled doom for Balor and his armies. An unnamed lieutenant and her companions entered a manse on the Blessed Isle: the controlling manse for the Sword of Creation, now commonly called the Realm Defense Grid. Nobody knows exactly how she managed to activate the Sword, but it gave her control over a Creation-wide network of war manses which she used to obliterate the invading fae armies. The only thing the world knows about her desperate gambit is that none of her companions survived the attempt.

After destroying the fey, she seized power for herself and founded the Realm, becoming the Scarlet Empress.