From Wikipedia

The First Americans

Scientists believe that the Inuit people of the high Arctic came to North America much later than other native groups, as evidenced by the disappearance of Dorset culture artifacts from the archaeological record, and their replacement by the Thule people.

During the thousands of years of native inhabitation on the continent, cultures changed and shifted. Archaeologists often name different cultural groups they discover after the site where they are first found. One of the oldest cultures yet found is the Clovis culture of modern New Mexico. A more recent example is the group of related cultures called the Mound builders (e.g. the Fort Walton Culture), found in the Mississippi river valley. They flourished from 300 BC to the 150s AD.

The more southern cultural groups of North America were responsible for the domestication of many common crops now used around the world, such as tomatoes and squash. Perhaps most importantly they domesticated one of the world's major staples, maize (corn).