Population change can be interpreted as the result of the continuous confrontation and adaptation between the forces of constraint and the forces of choice. Forces of choice are the ability to modulate and control behaviors that have demographic consequences, such as entering into a reproductive union; having children; protecting and enhancing health with adequate nutrition, housing, and clothing; moving and migrating from one place to another. Modern demography has been characterized by an acceleration with a variety of geographical patterns, and this variety increases the smaller the scale of analysis. This chapter outlines the nature of the demographic systems prevailing in different parts of the world in the eighteenth century. It presents the factors that determine a change or a transformation of a demographic system, therefore affecting population development. To define demographic transition as the process that has reduced mortality and fertility from the high pre-nineteenth-century levels to the low ones that prevail nowadays in Europe, America, and East Asia.

This chapter discusses all forms of market exchange including everything from local trade in which very little transport of goods might be involved to trade over long distances, both inside and outside the Roman empire. It talks about what is now known about patterns of trade in various commodities, about the social and institutional mechanisms by which trade was conducted, and about the role of governments. The main geographical patterns of long-distance trade were determined by the location of these markets and of the centres of production or supply. Many merchants avoided specialization, and for this reason among others it is artificial to discuss Roman trade commodity by commodity. It remains true that reasons of technology and of social structure prevented the Romans from replacing their agrarian economy, in which the mass of the population lived not much above subsistence level, with a more dynamic system.