The Rampart Trilogy

 Fiction by M.R. Carey

https://www.barnesandnoble.com/ book2/ book3

This is a three-book series set in the post-apocalyptic future. (It's a different end-of-the-world scenario than the one Mr. Carey detailed in The Girl With All the Gifts. It seems this guy can think of many different ways for society to collapse in upon itself.)

Koli is a young man in a small place called Mythen Rood, living three hundred years after the Unfinished War killed millions and scattered the survivors. Aged almost fifteen, Koli is hoping to be chosen as a Rampart, the select group of people who both rule and defend his village by means of the few pieces of tech they command. But when the time of choosing comes, he is surprised by the outcome.

These books were absorbing to read; I liked them a lot!

I also read by this author: Fellside