One of the topics currently under discussion on a writing forum is theme. The post’s author stated that she sometimes feels as if she’s writing the same book over and over again. I can certainly relate, having recently taken note of the overwhelming presence of various kinds of oppression in my stories. You can probably make a good case for the presence of a dominant theme in the work of many writers. After all, any theme you choose — or that chooses you — can probably be explored endlessly in all its complexity and variability.
My particular concern, when looking over my published work, with an eye to writing projects still in process, is whether I am, unconsciously, telling the same story over and over, merely changing the settings and the names of the characters. I can see that I concentrate on the character suffering oppression, whether as a prisoner, a slave, or someone caught up in the gears of a society suffering the strains of unanticipated and extreme changes.
But what about the people or the social forces responsible for the oppression? They are the source of the novel’s necessary conflict, but I think a closer examination of my published work might show that I sometimes allow them to remain shadowy figures that aren’t fully developed. The source of conflict in a novel can’t be an abstraction; the protagonist must be doing more than punching the air against a mysterious figure that fails to reveal itself.
There are many ways to approach theme, and that includes discovering it after you’ve written the first draft, and then developing it more fully. Chuck Wendig, bless his foul-mouthed heart, offered some valuable views of theme in an old post. Go there. http://terribleminds.com/ramble/2011/09/26/25-things-writers-should-know-about-theme/