About 200 BC, people living in the Northeast and Midwest (from modern New York to Missouri and from Wisconsin to Mississippi) formed a culture called the Hopewell culture (named after a farm where archaeologists first dug it up). Nobody knows for sure where the Hopewell culture got started - maybe these people lived first near Lake Erie and then expanded west and south, or maybe they lived first near Lake Superior and then expanded east and south. Or possibly they didn't move around at all, but just invited towns near them to join their network. Most of the towns and villages of the Hopewell culture were along the banks of rivers, and traders and rulers used the rivers to travel between the towns in canoes. The Hopewell people were mainly farmers, living on squash, sunflower seeds, and various grasses like wild rice, but they did not yet grow much corn, because it wouldn't grow well so far north. They built a lot of big earth mounds in various shapes, but nobody is sure what the mounds were for - maybe for burials.
Around 400 AD, the Hopewell culture collapsed. Nobody knows why this happened. It may have something to do with changes in the environment. After several hundred years, the Mississippian culture took its place.