Human prehistory in North America is most commonly believed to begin with the great nomadic migration over Beringia, a land bridge between eastern Siberia and Alaska that came into existence roughly 25,000 years ago, when the Wisconsin glaciation had locked away enough of the world's water to lower eustatic sea levels by over 60 metres. Also known as the Bering land bridge, Beringia escaped glaciation along with Alaska because the dominant southwesterly winds had already lost their moisture over the glaciation further south. Beringia extended over most of the width of the modern Bering Sea, and is generally believed to have remained in existence for several thousand years.
The native peoples of North America can be genetically traced to some 70 founding tribes. The native peoples of North America still show a strong common genetic heritage with the native peoples of eastern Asia, with the northernmost Inuit tribes having the strongest genetic and linguistic links with the native peoples of eastern Siberia.
Existing glaciation, along with the dominant north-south geographic features of the region, strongly influenced subsequent migrations into first easterly and then banded southerly movement which reached as far south as Central America. In North America, Pacific coastal nations from Alaska to Central America quickly became genetically distinct from native cultures on the east side of the continental divide. The earliest known North American artifacts date back to 12,000 BCE, only about five millennia after the height of the of the Pleistocene Ice Age; however, much of the early evidence for human occupation may have been eradicated by rising sea levels. The Clovis big game hunting culture, named for a distinctive spearpoint style originally found at Clovis, New Mexico, is usually considered the earliest and most widely distributed identifiable culture of North America, and may even have populated parts of South America. One alternate model posits a single, small pre-Clovis southerly migration along an ice-free corridor at the continental divide.
South American prehistory and native diversity and genetics does not fully match the pattern of North American migration, and may even include independent Pacific colonisation. A detailed examination of South American prehistory lies outside the scope of this article.
In North America, aboriginal culture evolution is generally divided into five stages: Lithic, Archaic, Formative, Classic, and Post-Classic (Willey and Phillips, 1958). More specific and accurate regional and chronological division has since been developed, but the broad stages still serve for an overview.
The Lithic stage, dating back from Bering migration through to around 8000 BCE, is typified by nomadic hunter-gatherer cultures with big game hunting adaptation. Its representative culture is the Clovis culture, although it also includes the Paleo-Indian and Folsom groups.
Dating to about 1000 BCE, the Archaic stage covers those cultures which have developed an increasing reliance on the gathering aspect of food supply, even to the point of developing a nomadic agriculture. The smaller stone tools associated with harvest are typical of these cultures.
The Formative state is associated with stabilised, village-based agricultural cultivation, with many cultures having developed basic irrigation techniques. Geographically, its relics are most frequently found among tribes in a broad swath along the Mississippi River valley through Florida, Texas, and parts of Mexico. It dates approximately to 500 CE.
The so-called North American "early civilisations" dating between 500 and 1200 CE are considered to be part of the Classic stage. Best known among these are the Toltec and early Maya.
Finally, the Post-Classic stage, dating from 1200 CE until European colonisation, included the great civilisations of central and the northern parts of South America, as well as such governmental bodies as the North American Iroquois Nation.