AMERICAN HISTORY and NATIVE AMERICANS
It is not definitively known how or when Native Americans first settled the Americas and the present-day United States. The prevailing theory proposes that people from Eurasia followed game across Beringia, a land bridge that connected Siberia to present-day Alaska during the Ice Age, and then spread southward throughout the Americas. This migration 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 melting glaciers. These early inhabitants, called Paleo-Indians, soon diversified into hundreds of culturally distinct nations and tribes.
This pre-Columbian era incorporates all periods in the history of the Americas before the appearance of European influences on the American continents, spanning from the original settlement in the Upper Paleolithic period to European colonization during the early modern period. While the term technically refers to the era before Christopher Columbus' voyage in 1492, 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 centuries after Columbus's initial landing.