What happened to the Mound Builders?

Answer 1

The Mound Builders were various groups of prehistoric inhabitants of North America who built mounds. The mounds of North America, according to archaeological research, were built over a long period of time, about 5,000 years, by different types of societies.

Mound Builder or Mound People is also a general term referring to the Native North American peoples who constructed various styles of earthen mounds. In the eastern US, these included the Archaic, Woodland, and Mississippian cultures.

http://www.infoplease.com/encyclopedia/science/mound-builders.html

Answer 2

It is believed that many of the Mound Builders fell victim to disease. This occurred when the Conquistadors arrived. They brought with them diseases that the Mound Builders could not fight off.