Changes and continuities from the classical to the post-classical cover a wide range of political, cultural, religious and economic shifts as populations grew and societies became more complex. The classical empires of Rome, Han China, Gupta India and Archaemenid Persia fell due to external and internal forces and were replaced by the larger empires of the post classical Byzantine; Tsui, Tang and Song in China and the Caliphates in Persia. Only India did not return to an over reaching centralized empire. During the post-classical Dar el-Islam united much of Eurasia with a single religious adherence to Islam. Also, the largest empire the world was ever to see, the Mongols, rose during the post classical period. These large, complex empires altered governments and economies, more by scale than bringing about any revolutionary changes. Culturally people became more urban and with that urbanization the trends toward the loss of freedom for women and the gulf between rich and poor continued to widen. Religions that started in the Axis Age, the period of turmoil during the collapse of empires, such as Christianity, Buddhism and Hinduism, found new adherents as their followers traveled the increasingly global land and maritime trade networks. Islam arose at the beginning of the post-classical period and in a short 200 hundred years enveloped all of southern Eurasia and north and east coastal Africa.
From the classical to the post classical new larger empires arose. In China the new post-classical empires of the Tsui, Tang and Song looked to their past classical empire, the Han, in which to recast themselves. China returned to the political and cultural practices abandoned during the Warring States Period. In China we see continuities in political, cultural, and religious practices. Imperial structure is restored and the examination process for hiring bureaucrats is expanded to include any male who can pass the local,