The great classical cultures of Eurasia created separate identities, but each of these cultures also contained important elements that other peoples adopted. In the classical and post-classical periods (600 BCE to 1450 CE), the peoples and cultures of this vast area had consistent and enduring interactions. What were the three main causes or sources of this new integration of Eurasia? What were three important consequences or effects? What made these causes or sources and consequences or effects so important?