"Since progress is the rare exception, and not the rule, among the communities of mankind, it is less important to speculate about the reasons for its cessation among the ancient Egyptians than to observe how the technological advances made in the Near East became by degrees more widely diffused until they penetrated Europe. Neither Mesopotamia nor Egypt had the resources which would have enabled it to develop its civilization on a basis of autarky. They had never been self-contained as regards timber or metals or even ivory: in the second millenium B.C. the development of larger ships and better organized land transport encouraged greater efforts to satisfy their needs by importations. In exchanging the products of their superior technology for raw materials they stimulated imitation. Moreover, in ancient as in modern times the needs of trade often stimulated the desire for conquest, which likewise left its mark upon the life of neighboring peoples long after the tide of conquest had receded. Aggression then provoked counter-aggression: some barbarian intruders were eventually absorbed into the life of the two empires, others clashed with them, and kept their independence."