Hypothesized Western and Eastern world-systems of the Late Bronze Age collapsed in the twelfth and eleventh centuries b.c. before a new phase of integrations occurred in these areas (western Asia, northern Africa, and southern Europe on the one hand; China on the other). This article argues that in the first millennium b.c ., these two world-systems experienced three long cycles marked by hegemonic transitions between competing regions. The recessions that we observe stemmed partly from climatic deteriorations on varying scales around 800, 400, and 200 b.c. The growth of networks and states was furthered by technological, institutional, and ideological innovations. A number of empires arose in western Asia, which aimed at controlling spaces and peoples between the Mediterranean and the Persian Gulf. An Indian world-system developed, which partly merged with the western system from the fourth century b.c . From the third century b.c ., changes in western Asia, China, and India and the extension of exchange networks favored the opening of land routes across central Asia and maritime routes in the Indian Ocean and China Seas. The rise of new centers in the western Mediterranean region accompanied a growing integration of Europe into the Western system. The three world-systems identified probably fused into a single worldsystem in the first century a.d ., when the rise of exchange networks led to an interdependence of their various regions.