Unbeknownst to most, I spend hours thinking about a thousand and one background aspects. Half my book is written on random trains of thought. Yes, I should try and plan my plot instead of pantsing it. But these details, this understanding of my own world isn’t there from the beginning.
In many ways, I’m an archeologist in my own works, using what I can find to piece the puzzle together. The spontaneous trains of thought can be moved around to make a scene and that’s very much how it’s done.
I’ll follow one story for a bit and then discover that there’s a whole other aspect that I can expand upon, like another cave drawing that explains the first one. It’s a very chaotic method but it’s how everything is both found and made.
No history is wholly linear. There’s gaps. Some of the bridges are inferences, others, works of fiction. The background lore that builds from inference builds upon itself and sometimes creates new branches that have to be researched somewhere else.
History is written as it happens today. However, due to constraints, someone a few hundred years later will have read some diaries about today and make their own “truth” about what they see as history. Then someone will find six or twelve of those “studies” and make an overarching piece that explains it all in one go.
History is found and inferred, sometimes made from fiction. My book, the world that exists around those characters is no different and little by little, I as their creator, am piecing together their history