The city is a technology unto itself. As such, it has inherent qualities that compel certain applications and dissuade or forbid others. The primary quality, which it uses as a foundation for all of the rest, is centralization.
The city centralizes all that it can. It centralizes population, food supplies, water supplies, economic functions, political power, cultural production and diffusion, religious influence- any and all means to establish, maintain and exercise domination over others. This is what makes the city so vital to Empire.
The city exerts this centralizing influence through an expression of convenience that, after a time, feels like the pull of gravity itself upon those so much smaller than it. There is a dense core at its center, from which that pull comes and to which all it attracts goes, and into orbit around it are an increasing array and number of bodies that settle around that core. These rings, and the bodies within them, enter into relationships of push and pull with the core and each other. When these ties are stable, their cumulative power strengthens that pull and accelerates the process; when unstable, they threaten to disrupt and destroy the city altogether, rending it asunder in the hope of starting over as the core of a new city.
The city's hunger, like that of a rapacious vampire, only grows as it does. It consumes the produce of the productive countryside, first its surplus and then its produce. It consumes the people of the countryside, first its excess and then its entirety. Then it installs thralls (who are often Thralls) to transform the countryside into a meek reflection of itself, making inhuman changes to achieve inhumane ends to create farms run by automata--zombies or robots, take your pick; the result is the same--and not by Mankind for human (and humane) ends. It creates a miasmic illusion that the city is all that matters, when the city is actually superfluous and expendable, and it does this through the increasing of the perception of time in those that dwell within its clutches. Meanwhile, the city cannot feed itself, clean itself, keep itself hydrated or otherwise do what is required of any lifeform without the aid--willing or not--of the productive countryside and the natural world that it is lawfully and harmoniously based upon, yet often disdains and abuses without pity or remorse.
We never needed to live this way. We certainly don't need to do so now. We should, instead, acknowledge that freedom comes from acknowledgement that being decentralized and distributed is the proven path to autonomy and freedom due to its support for and encouragement of individuality at all levels. Empire is all about centralization, with the domination and control that comes with it; Mankind is at its best when decentralized and distributed, and remaking our world into a Civilization that builds upon this superior model is one big way to make Empire fall.