The country that came to be the United States had a small, dispersed native population at the time of initial European discovery, totaling perhaps 800,000 people, most organized in small tribal units.
There was great diversity among American Indian cultures. Several hundred dialects were spoken along the coast of California alone. The Pueblo, who lived in what is now New Mexico and who were probably influenced culturally by the Aztecs to the south, resided in permanent towns and constructed extensive irrigation systems. The Piutes of the Great Basin lived in temporary thatch dwellings and pursued a seminomadic existence based on available wild edible vegetation and small game. The Inuit, or Eskimos, who were the most recent of the pre-European arrivals, shared close cultural ties with Inuits in Greenland and Siberia.
Although American Indians represented a barrier to the expansion of European settlement at times, for the most part their impact was minimal. Many died of imported infectious diseases such as smallpox and measles before they experienced direct contact with the Europeans. The Indians made important contributions to the arriving Europeans, especially during the first decades of settlement. But most often they were killed or shunted off to reservations in the West. As the settlement frontier moved westward, so did the American Indians and their reservations.
Source: U.S. Department of State