The social, cultural, and political systems developed in India, China, and Rome all had enormous impact on neighboring peoples whose cultures were originally not as technologically advanced. Some of the mechanisms for cultural spread were similar in all three cases, but differences were important as well.

In the case of Rome and both Han and Tang China, strong states directly ruled outlying regions, bringing their civilizations with them. India’s states did not have comparable bureaucratic reach. Outlying areas tended to be in the hands of local lords who had consented to recognize the overlordship of the stronger state. Moreover, most of the time India was politically divided.

The expansion of Indian culture into Southeast Asia thus came not from conquest and the extension of direct political control but from the extension of trading networks, with missionaries following along. This made it closer to the way Japan adopted features of Chinese culture, often through the intermediary of Korea. In both cases, the cultural exchange was largely voluntary.