cultures
political structures
setting (and, we agreed, this is a wide category in itself)
boundaries (which relates to setting and character backstories)
character backstory as tool for exploring limitations and responses to world >>> Boundaries of the world
rules (internal logic)
genre (which affects the way you present the world and also the rules of it)
social constructs
political structures
incentive
pressure/outside forces
scope of characters
problems e.g. post apocalyptic