We’ve got a bit of dieselpunk in our CorpWars world, too. The enclave city-states do not use fossil fuels, though. They are most advanced in energy generation and storage.
They are survivalists, and I’d like to use a quote (from the game Alpha Centauri) that describes their most popular ideology:
“Learn to overcome the crass demands of flesh and bone, for they warp the matrix through which we perceive the world. Extend your awareness outwards, beyond the self of body, to embrace the self of group and the self of humanity. The goals of the group and the greater race are transcendent, and to embrace them is to achieve enlightenment.”
— Sheng-ji Yang, “Essays on Mind and Matter”