What were the purpose of the earthworks build by cultures of eastern north america

In the 16th through 19th centuries, Europeans and Americans generally thought that a people other than one related to the historic Native Americans had built the mounds. The namesake cultural trait of the Mound Builders was the building of mounds and other earthworks

In my honest opinion , i’d say franklin d roosevelt was a president that impacted our nation , i say this because fdr is voted among top three best us presidents and he was the longest serving president by 3 terms , usually presidents only supposed to have two terms increments of 4 years , equivalent to 8 years total before election time. and he established the fdic , through the 1933 banking act and he established the us , social security system , during his presidency, and established a national minimum wage , through the fair labor standards act , fdr led the allied coalition to victory in wwii and he played a major role in the creation of the united nations.