As mentioned in my initial post, when I started worldbuilding I used a few ideas that I'd had in the back of my mind since the early 1990s. They were only vague ideas and certainly not something that could be turned in to a game world. In fact, the stories I'd written back then were more steampunk than what I'm currently running (though I think it was probably about another ten years since I'd first encounter the word steampunk). Generally the world I'm now running could be considered the ancient past of the (fragments of) stories I'd previously written. The world has a few basic concepts, some of which I won't go in to as the players don't know about them yet!