What's going on in the Postclassical Era?

The postclassical era featured the restoration of political and social order. Islamic faith overcame the Sassanid empire. The Sui and Tang Dynasty overcame the regional kingdoms. But in India, central rule did not return. In Western Europe, centralized control returned briefly. The restoration allowed societies to engage in long-distance trade and exchange. Agriculture also improved as well. Increased trade and manufacturing led to new innovation.. Also, Islam and Christianity became religious foundations for empire.