After 800 AD the Mississippian culture developed all along the Mississippi and the Missouri valleys. Now many people lived in towns. They built temples and palaces on top of big earth mounds. They had wooden fortification walls around their towns, with walkways at the top. Like the Hopewell people, the Mississippian people also traded
and traveled using the rivers, especially the Mississippi river. But the Mississippian people did grow corn, and they lived mainly on corn, beans, and squash. They built bigger mounds than the Hopewell people, too, and like the Maya in Central America they
built buildings on top of their mounds - temples to their gods, and palaces for people to live in, and meeting houses.
Further east, the Cherokee people also began to live in towns and villages and farm a lot of their food, and traded up and down the rivers. In the north, at the headwaters of the Mississippi basin, the Cree and the Sioux continued to gather wild rice, though they too built burial mounds.
A global warming period which began around 1000 AD and lasted until 1300 AD caused a lot of people to look for a better place to live during this time. The Inuit moved south from the Arctic circle into Labrador. The Vikings left Greenland entirely and moved back to Iceland and Scandinavia. The Iroquois moved north along the Susquehanna river (from modern Maryland to modern New York State and Canada). The Pueblo people in the south-west left their towns in northern Arizona and Colorado about 1200-1300 AD and moved south.
Not everyone in North America lived in towns and farmed at this time. Some people who lived in the north, like the Iroquois, kept on living in a Late Woodland culture until they met Europeans in the 1500s. The Algonquin, the Sioux, and the Cree, further north than the Iroquois, remained in a Late Archaic culture into the 1500s. On the northern Pacific coast, the Chinook were living in a Late Archaic culture into the 1700s AD. In the far north, the Inuit were living in a Middle Archaic way into the 1900s AD.
And the people who moved to the Great Plains, like the Navajo, the Blackfoot, and the Ute, mostly didn't start farming, because the grasslands would not support the kind of farming they knew how to do. Instead, they got most of their food from buffalo hunting. They traveled from one place to another as nomads following the buffalo, carrying their things and using dogs to pull a travois with their tipi on it.
After the warming period, about 1350 AD, there was a global cooling period known as the Little Ice Age. Other people moved around during this time. For instance, the Navajo and the Apache moved south out of Canada into the southern Great Plains at this time. The Mississippian and Cherokee people didn't move anywhere. But around 1400 AD, something does seem to have changed in the Mississippi Valley. People stopped building mounds, and a lot of the bigger towns seem half-abandoned. People seem to have moved out to the countryside, maybe doing more hunting and gathering and less farming. This might be because of the warming period, or it might be a political collapse, or something else. In any case, at the time that the first Spanish explorers arrived in North America, around 1500 AD, people were not very well prepared to fight them off.