I’m discovering that creating a world is much like creating a character. You start with parameters. As the story progresses, the world takes on a life of its own and “tells” the writer other parts. A character might suddenly say something about his/her past to another character, that you didn’t know before. . .in world building, a character suddenly says something about the world that you never knew before.
Example: In book two, Neri’s struggling with grief and rage. She considers how Reyism handles these things and tada. . .a ceremony I never knew of before! There it is, and of course that’s what they do. 7 billion people died of a plague created, basically through hate. Braedon Rey would naturally create a forgiveness ceremony to help people cope.
This is one of the best parts of writing.