Between civilizations, in time and space, most human communities have been self-sufficient. Whether as food gatherers, pastoral people or cultivators of the soil they have produced and consumed the food, shelter, clothing, implements and weaponry required for their survival.
The city, whether a political capital or a center of trade and commerce, was sharply separated from the self-sufficient countryside. The city, by its very nature, could not be self-sufficient. Food, building supplies and raw materials were not produced inside the city limits, but must be produced in the hinterland from which they were transported to the cities. City dwellers devised means of paying for the production, transportation and marketing of these necessary imports. The countryside can and does exist independently of the city because it can provide the goods and services on which its existence depends. The city, on the contrary, cannot exist without the supplies produced in the hinterland and transported to the city.
Urban centers of civilization have for their background a pastoral and agricultural source of food supplemented by fabrication, merchandising and financing. Instead of the occupational uniformity of the countryside, the city offers a wide range of occupations, increased productivity, quick and substantial profits resulting in a build-up of capital on one side and enlarged consumer spending on the other. Consequently the successful competitor in the race for supremacy develops productivity, accumulates wealth, expands capital spending, enlarges the scope of the arts, thereby augmenting the city's attractiveness to business enterprise and migrants from the hinterland.
As the capital city grows in wealth and opportunity it requires larger imports of food, raw materials, building supplies, manpower. Growing internal need leads to greater external expansion. Economic, political, administrative and cultural needs not only increase the demands of the city on its existing hinterland, but they lead to a demand for a more widely extended hinterland.
The countryside is the goose that lays the golden eggs. The city gathers, guards and eventually consumes the eggs or converts them into capital forms and lives in part on this unearned income.
The city is the mecca which attracts by its wide ranging opportunities. It is also the center in which policies are made and offered to the countryside as normal facts of life. The countryside accepts city leadership including a higher wealth-power per capita ratio for the city.
Cities, with their accumulations of population and wealth, are walled or otherwise defended. When danger threatens, countrymen often move inside the walls until the danger abates.
Cities and city life increase and expand with the growth and expansion of civilization. Cities are the centers from which civilization grows and expands. Historically, a number of cities or city-states have competed for survival and supremacy. One by one they have dropped out of the race or have been out-classed, defeated and/or absorbed by the victors in the competitive struggle. One location proved to be more advantageous than others. The inhabitants of one locality were more skillful, more far sighted than those of rival localities. Many competed. Eventually one survived the final round of struggle, emerging as the nucleus of an expanding empire and a maturing civilization. A protracted conflict raging first in Italy and later in the entire Mediterranean basin, resulted in the Roman Empire and eventually in Roman civilization. A similar series of struggles, this time planet-wide, gave the British a taste of planetary supremacy in the nineteenth century and opened the door wide enough to give the United States oligarchy a glimpse of an American Twentieth century, which never eventuated.
Occupational differences within the city led to a differentiated class structure. As the trading city developed, businessmen eventually played a dominant role because they were able to command larger incomes, accumulate more wealth and offer more aggressive leadership.
Nuclei of both empire and civilization were associated with a cluster of allies, client states, dependencies and colonies related to the center by economic interests and by diplomatic bargains or political controls. They paid tribute or taxes as the price of living within the defense perimeter of the ruling elite, conforming to the chief aspects of its culture and in emergencies taking refuge inside the city defenses.