According to the theory of the Settlement of the Americas, migrations of humans from Eurasia to the Americas took place via Beringia, a land bridge which formerly connected the two continents across what is now the Bering Strait. The number and composition of the migrations is still being debated.
Falling sea levels created the Bering land bridge that joined Siberia to Alaska, which began about 60,000–25,000 years ago.
The minimum time depth by which this migration had taken place is confirmed at 12,000 years ago, with the upper bound (or earliest period) remaining a matter of some unresolved contention.
Three major migrations occurred, as traced by linguistic and genetic data; the early Paleoamericans soon spread throughout the Americas, diversifying into many hundreds of culturally distinct nations and tribes. The North American climate finally stabilized by 8000 BCE; climatic conditions were very similar to today's.
This led to widespread migration, cultivation of crops, and subsequently a dramatic rise in population all over the Americas.
The big-game hunting culture, labeled as the Clovis culture, is primarily identified with its production of fluted projectile points. The culture received its name from artifacts found near Clovis, New Mexico; the first evidence of this tool complex was excavated in 1932. 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).
Numerous Paleoindian cultures occupied North America, with some arrayed around the Great Plains and Great Lakes of the modern United States of America and Canada, as well as adjacent areas to the West and Southwest. According to the oral histories of many of the indigenous peoples of the Americas, they have been living on this continent since their genesis, described by a wide range of traditional creation stories. Other tribes have stories that recount migrations across long tracts of land and a great river, believed to be the Mississippi.
Genetic and linguistic data connect the indigenous people of this continent with ancient northeast Asians. Archeological and linguistic data has enabled scholars to discover some of the migrations within the Americas.
The Folsom Tradition was characterized by use of Folsom points as projectile tips, and activities known from kill sites, where slaughter and butchering of bison took place. Folsom tools were left behind between 9000 BCE and 8000 BCE.
Chicken pox and measles, although by this time endemic and rarely fatal among Europeans (long after being introduced from Asia), often proved deadly to Native Americans. Smallpox proved particularly fatal to Native American populations.
Epidemics often immediately followed European exploration and sometimes destroyed entire village populations. While precise figures are difficult to determine, some historians estimate that at least 30% (and sometimes 50% to 70%) of some Native populations died after first contact due to Eurasian smallpox.
One element of the Columbian exchange suggests explorers from the Christopher Columbus expedition contracted syphilis from indigenous peoples and carried it back to Europe, where it spread widely.[50] Other researchers believe that the disease existed in Europe and Asia before Columbus and his men returned from exposure to indigenous peoples of the Americas, but that they brought back a more virulent form.
In 1618–1619, smallpox killed 90% of the Native Americans in the area of the Massachusetts Bay.
Historians believe many Mohawk in present-day New York became infected after contact with children of Dutch traders in Albany in 1634. The disease swept through Mohawk villages, reaching the Onondaga at Lake Ontario by 1636, and the lands of the western Iroquois by 1679, as it was carried by Mohawk and other Native Americans who traveled the trading routes.
The high rate of fatalities caused breakdowns in Native American societies and disrupted generational exchanges of culture.
Between 1754 and 1763, many Native American tribes were involved in the French and Indian War/Seven Years War. Those involved in the fur trade in the northern areas tended to ally with French forces against British colonial militias. Native Americans fought on both sides of the conflict. The greater number of tribes fought with the French in the hopes of checking British expansion. The British had made fewer allies, but it was joined by some tribes that wanted to prove assimilation and loyalty in support of treaties to preserve their territories. They were often disappointed when such treaties were later overturned. The tribes had their own purposes, using their alliances with the European powers to battle traditional Native enemies.