<P> It is not definitively known how or when the Native Americans first settled the Americas and the present - day United States . The prevailing theory proposes that people migrated from Eurasia across Beringia, a land bridge that connected Siberia to present - day Alaska during the Ice Age, and then spread southward throughout the Americas over the subsequent generations . Genetic evidence suggests at least three waves of migrants arrived from Asia, with the first occurring at least 15 thousand years ago . These migrations may have begun as early as 30,000 years ago and continued through to about 10,000 years ago, when the land bridge became submerged by the rising sea level caused by the ending of the last glacial period . These early inhabitants, called Paleoamericans, soon diversified into many hundreds of culturally distinct nations and tribes . </P> <P> The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences on the American continents, spanning the time of the original settlement in the Upper Paleolithic period to European colonization during the Early Modern period . While technically referring to the era before Christopher Columbus' voyages of 1492 to 1504, in practice the term usually includes the history of American indigenous cultures until they were conquered or significantly influenced by Europeans, even if this happened decades or even centuries after Columbus' initial landing . </P> <P> Native American cultures are not normally included in characterizations of advanced stone age cultures as "Neolithic," which is a category that more often includes only the cultures in Eurasia, Africa, and other regions . The archaeological periods used are the classifications of archaeological periods and cultures established in Gordon Willey and Philip Phillips' 1958 book Method and Theory in American Archaeology . They divided the archaeological record in the Americas into five phases; see Archaeology of the Americas . </P> <P> The Clovis culture, a megafauna hunting culture, is primarily identified by the use of fluted spear points . Artifacts from this culture were first excavated in 1932 near Clovis, New Mexico . The Clovis culture ranged over much of North America and also appeared in South America . The culture is identified by the distinctive Clovis point, a flaked flint spear - point with a notched flute, by which it was inserted into a shaft . Dating of Clovis materials has been by association with animal bones and by the use of carbon dating methods . Recent reexaminations of Clovis materials using improved carbon - dating methods produced results of 11,050 and 10,800 radiocarbon years B.P. (roughly 9100 to 8850 BCE). </P>

Three indian groups that lived south of what is now the united states