Final answer:
The Hopewell tradition transformed their environment by creating earthen mounds, which served ceremonial and religious purposes. While they did practice agriculture, mounds were their distinctive environmental contribution. Agriculture led to social changes in the Hopewell culture.
Step-by-step explanation:
The Hopewell tradition, prominent in the Ohio River Valley, transformed their environment chiefly through the creation of earthen mounds. These mounds had significant ceremonial purposes and were often a place for the veneration of ancestors, indicated by the burials found within them. While the Hopewell practiced agriculture and supplemented it with hunting and fishing, their notable contribution to the transformation of their environment was through these earthen mounds rather than through methods such as terraforming, terracing, or aquaculture.
Agriculture played a fundamental role in the development of the Hopewell culture and their society, but it was not the primary method by which they transformed their environment. The adoption of maize agriculture was a major reason for the cultural shift in the later Mississippian tradition, which did result in significant alteration of the environment.
Over time, the increasing availability of food due to the practice of agriculture and exposure to wealth through trade led to social transformations within Hopewell societies, as evidenced by the less egalitarian nature of these societies when compared to their hunter-gatherer predecessors.
Lastly, while ancient city-states and empires may have used methods such as tribute, intermarriage, and espionage to acquire territory peacefully, warfare was also common. However, this is not directly related to the practices of the Hopewell tradition, who are better known for their earthen mound-building rather than the expansion of their territory through war or other peaceful means.