Future histories offer another way to develop your world building. This is a big-scope approach, wherein you develop worlds and societies over multiple stories, building a sense of continuity and imagined history. You don't have to do it all at once; you can build it over time, as Larry Niven did with his Known Space stories, and Heinlein with his future timeline — and as I did with my Star Rigger universe, and many other authors have done with their books and stories.

When you develop a future history, you expand the scope of your thinking. Rather than chronicling just the actions of a few characters (or even the many characters who might appear in a single story), you're telling the tales of characters who may be separated by generations, and of worlds and societies that grow and change in relation to each other. You start to think in terms of chronologies and the onward march of history — of the "meta-story," the overarching story line that may gather numerous smaller tales in its sweep. Not that the individual stories have to be small, of course; but there's always a sense of a vaster story yet to be told, of which the current story offers but a glimpse.

Although I titled this future histories, there are of course alternate histories, as well, in which timelines have unfolded differently from the way they have in our world. In fantasy, there can be histories of times and worlds that never existed, though we may feel that they ought to have. Tolkien's Middle Earth, for example, encompasses a history far greater than the "brief" episode told in The Lord of the Rings.

Building the history of your own world is a long-term project. For some authors, it's a life-time project. If the idea appeals to you, think of it as something to work toward, as you learn to build the worlds for your more closely focused stories.