(If you've seen this elsewhere - yup, I'm posting this all over, because I want lots of ideas)
There is [Something You Can Cast As A Resource] in this world.
It is used for A, B, C.
This creates groups X, Y, Z.
-There are Direwolves in the world.
-They're used as goblin mounts, as elven watchwardens, and as allies for shapechangers.
-The goblin horde, the rangers of Alon, and the Black Fang mercenaries exist as a result.
-There is Skystone in the world; a mystical floating material.
-It's used to build flying castles, and burnt into tattoos.
-The floating city of the Rift, and the temples of the sky monks exist as a result.
-There is an Akashic Record in the world; an intangible record of all events.
-It is tapped into (shallowly) for knowledge by deep meditation, or by birthright in a select few (an inheritable trait).
-Because of this, meditation is the fundamental key to deeper education, and those born Readers are the natural nobility - but are tested for ability and cast out if they fail.
-The Chained Behemoth can be found in this world, a mile-long regenerating monster nailed to the earth.
-It's body is harvested continually for meat, for bone, for blood, and for reagents that allow one to take on properties of the beast itself.
-The city of the Behemoth, the cult of the Beast, and the bonesmith's guild exist as a result, among others.
What else is in this world?