A land being plunged into chaotic energies, wild superstition, massive prejudices and distrust. More of a campaign setting than anything else.
This is more of a concept applied to a particular setting than the setting itself, bear this in mind.
Not every prophecy needs to be meaningful to effect a game. In the Lord Dunsany play, The Golden Doom, a child's scrawl has an entire kingdom struggling to puzzle out what sinister prophecy it portends.