4 ideas
The shell is fired but launched at such velocity that it overshoots and goes into orbit around the Earth, and Schultze later dies alone in his sealed laboratory when one of his own carbonic-acid shells bursts. The Alsatian Marcel Bruckmann, who got inside Stahlstadt under a false name, reveals the city's secrets and takes it over for the people of France-Ville.
France-Ville is planned so that disease has nowhere to take hold: houses are low and detached, with no carpets or wallpaper, the streets are wide and the waste is swept out by sewers. There are also regular public disinfection routines. Here the city plan is itself the public health program, so healthy behavior is built into the physical layout instead of being left to individual choices.
Two heirs receive equal shares of one inheritance and the same industrial technology, yet one builds a city for health and the other builds an arms factory. Holding the resources constant shows that it is the builder's values, not the wealth or the technology, that decide whether industrial power improves life or destroys it.
Stahlstadt is divided into sealed sectors, and each worker knows only his own task and cannot enter the other sectors, while authority converges on Schultze's hidden Central Block. This secrecy protects the city's weapons, but it also reduces workers to replaceable components with no understanding of the whole.