The Middle Ages from the tenth century onward brought striking changes to the economic and political environment of the Western World. Population expanded, regional and interregional commerce revived, new techniques were developed, and the classic institutions of both manorialism and feudalism changed beyond recognition.

A high rate of natural increase in population, although interrupted at times by wars, pillaging, and occasional famine or epidemic, was made possible by the abundance of virgin land. Sporadic waves of immigration supplemented the natural growth until the crowded manors spilled over into new arable lands on existing manors or surged outward to found entirely new manors on virgin lands in the wilderness. Sparse settlements in the frontier areas contrasted with dense agglomerations on the older sites. During the three centuries which began the second millennium a.d., this extension of the boundaries of settlement was destined to convert Western Europe from a vast wilderness into a well-colonized region.

Co-extensive with population growth, commerce began to push outward, spreading and blossoming along with the new settlements. Northern Europe set up brisk internal trade, which expanded with time to the classic lands of the Mediterranean. Southern Europe, with Venice in the lead, had begun before the tenth century to extend the limits and magnitude of trade throughout that region. Other Italian cities, notably Genoa and Pisa, quickly responded to the expanded commercial opportunities available, trading money, timber, iron and wood and metal products to the Moslems for spices, perfumes, ivory, fine textiles and oil.