The Post Classical period from 600-1450 CE saw the rise of new empires and political systems across Afro-Eurasia including the Umayyad Caliphate, Abbasid Caliphate, Byzantium, Tang and Song Dynasties in China, and the Delhi Sultanate. Trade networks expanded greatly along routes like the Silk Road, and the rise of the Islamic world united a large region culturally and economically. Major epidemics like the Black Death impacted populations, while nomadic groups like the Mongols had profound effects through their invasions and military power.