‘Civilization’ means urbanized society and cities have been the most dynamic irruptions in the history of the planet, which makes the relative paucity of focused theory on the topic rather mysterious.
Historian William H. McNeill goes some way to correcting the deficit in his essay Cities and their Consequences, perhaps the most brilliant analysis of the urban phenomenon since Jane Jacobs (although unfortunately hidden behind the subscription wall at The American Interest).
McNeill begins his succinct study with the key demographic fact that cities have always operated as population sinks (or pumps) and, at this level of description, as megaparasites, supported by continual inflows from fecund rural areas (villages). The process of urbanization is overwhelmingly the most consequential factor shaping local, regional and planetary demographic trends. Furthermore, because urban populations are incapable of feeding themselves directly, their mere existence operates as a stimulus to trade, placing a vector in history through the specialization of labour and commercialization of society.
McNeill writes:
A second and more massive conversion to market farming [than that of the Greeks and Classical Mediterranean] occurred in China, beginning about 1000 CE when the Song government decided to collect taxes in the form of cash. That decision compelled ordinary peasants to find something to sell in order to pay their taxes. By that time, thousands of barges and small sailing vessels floating up and down the rivers and irrigation canals of China had created a cheap and reliable internal transport system. Small differences of price for objects of common consumption—even of rice—thus made it worthwhile to carry everyday commodities long distances. Large-scale marketing of specialized crops ensued. Soon millions of peasants found it advantageous to buy the rice they ate and sell silk or some other specialized crop, thus assimilating their way of life to city folks' long-standing dependence on buying and selling to gain their daily bread.
China's wealth and skills shot upward as the advantages of specialization were unleashed on a massive scale, and other parts of the earth soon began to follow suit wherever safe and cheap water transport allowed. The Indian Ocean coastlands and Southeast Asia, together with the Mediterranean, Baltic and Atlantic shores of Europe, were the principal places where commercialized farming began to take off within the next two or three centuries.
As urbanization proceeds ...
Older forms of human society—peasant ways, with all their limitations and hardships—are being left behind. The future is surely going to be different. Exactly how different no one can yet say, but two principal factors appear to loom large at least in the short run.
One factor concerns the half of humankind still living on the land and still cultivating the soil. This half of humanity, overwhelmingly non-Western, is now increasingly aggrieved by poverty, monotony and hardship compared with the lure of urban wealth and comfort. These are the people who see their children hastening away toward the world's cities in hope of improving their lives—more often than not only to meet disappointment in pullulating urban slums. Inhabitants of those slums, without regular jobs or reliable sources of income, constitute the other major human factor of our times. That human mass constitutes a pool of active discontent far more strategically located than rural dwellers, since their frustration and anger can readily be mobilized against oppressors living in city cores where everything they sought still glitters unshared and unattainable, temptingly close at hand. In short, the phenomenon of the subproletariat is being globalized amid technological conditions well-suited to the rapid spread of demagogic manipulation.
The other principle factor is cultural mutation, at the level of religion in particular. In cities ...
... sectarian cohesion is under constant strain, for in urban settings the ubiquity of choice among beliefs becomes unavoidable. Joining a religious group becomes a deliberate act, departure a perpetual possibility. Lifelong stability and adherence to unquestioned, inherited custom, nearly universal in village life, is unattainable under such circumstances. Instead, the very fragility of bonds invites a fevered intensity among successful sects. Demanding more from true believers and dividing them more sharply from outsiders are what sustain urban sects as their leaders seek to make it more difficult to abandon fellowship. Is it any wonder, therefore, that what is often termed "fundamentalist" religion is overwhelmingly an urban phenomenon?