I’m currently writing a book where there is a large explosion in Mid-USA, in the year 2025. Following this, there is a world war that diminishes the US population to ~70 million people. There is a group of kingdoms that form in the present-day Colorado area due to its centralized location that was away from most of the radiation and some of the devastation.
The book itself takes place in the year 2178. In this area at this time, I imagine that any coal or metal mines have been depleted and drilling for oil is nearly impossible due to the large machinery required. Much of the easily harvestable metal from the old cities has been used for weapons or structures. My current view is that wind/water/steam power would be the primary source of energy, and guns would mostly be only in the hands of the upper class due to their resource-guzzling nature. The civilizations are more unstable, with less focus on art and recreational activities, and more focus on surviving the warring kingdoms, weather, etc.
(Note: I initially said it would be feudal, but upon discussion, I have realized that that might not be entirely accurate. There would be Kings and Queens, with a large lower class and small upper/middle classes, but not feudal necessarily.)
My main question is this: Given the parameters above, what types of technology would be present?
Feel free to ask if you have any questions!
(Edited to improve clarity and accuracy)