This may be new information to some readers, but I’ve mentioned several places before that the Mistborn series was pitched to my editor as a sequence of three trilogies. Past, present, and future—epic fantasy, urban fantasy, and science fiction; all with the running thread of the magic system.
I want to commit myself to that but don’t want to dig into the second Mistborn trilogy for quite a while with everything else on my plate right now. I still want to prep people for the idea that Mistborn is going to be around for a while, and they are going to be seeing more books. I didn’t want it to just come out of nowhere at them in ten years or whenever I get to it. So I decided to do some interim stories.
One of the things I’d been playing with was the idea of what happened between the epic fantasy and the urban fantasy trilogies. We have some very interesting things happening in the world, where you’ve got a cradle of mankind created (by design) to be very lush, very easy to live in, so a great big city could grow up there relatively quickly; civilization could build itself back up over the course of just a couple of generations. Yet there would be very little motivation to leave that area at first, which I felt would mean that you’d end up with this really great frontier boundary. The dichotomy between the two—the frontier and the quite advanced (all things considered) city in the cradle of humanity—was very interesting to me. So I started playing around with where things would lead.
To worldbuild the urban fantasy trilogy coming up, I need to know everything that happened in the intervening centuries. Some stories popped up in there that I knew would happen, that would be referenced in the second trilogy. So I thought, why don’t I tell some of these stories, to cement them in my mind and to keep the series going.
I started writing The Alloy of Law not really knowing how long it would be—knowing the history and everything that happened, but not knowing how much of it I wanted to do in prose form. Things just clicked as they sometimes do, and I ended up turning it into a novel, and then a series of novels.