Since the end of the 15th century, the migration of Europeans to the Americas has led to centuries of population, cultural, and agricultural transfer and adjustment between Old and New World societies, a process known as the Columbian exchange. As most Native American groups had historically preserved their histories by oral traditions and artwork, the first written sources of the conflict were written by Europeans.
At the time of the first contact, the indigenous cultures were quite different from those of the proto-industrial and mostly Christian immigrants. Some Northeastern and Southwestern cultures, in particular, were matrilineal and operated on a more collective basis than the Europeans were familiar with. The majority of Indigenous American tribes maintained their hunting grounds and agricultural lands for use of the entire tribe. Europeans at that time had patriarchal cultures and had developed concepts of individual property rights with respect to land that were extremely different. The differences in cultures between the established Native Americans and immigrant Europeans, as well as shifting alliances among different nations in times of war, caused extensive political tension, ethnic violence, and social disruption. Even before the European settlement of what is now the United States, Native Americans suffered high fatalities from contact with new European diseases, to which they had not yet acquired immunity; the diseases were endemic to the Spanish and other Europeans, and spread by direct contact and likely through pigs that escaped from expeditions. Smallpox epidemics are thought to have caused the greatest loss of life for indigenous populations. William M Denevan, noted author and Professor Emeritus of Geography at the University of Wisconsin-Madison, said on this subject in his essay "The Pristine Myth: The Landscape of the Americas in 1492"; "The decline of native American populations was rapid and severe, probably the greatest demographic disaster ever. Old World diseases were the primary killer. In many regions, particularly the tropical lowlands, populations fell by 90 percent or more in the first century after the contact. "
Estimates of the pre-Columbian population of what today constitutes the U.S. vary significantly, ranging from William M Denevan's 3.8 million in his 1992 work The Native Population of the Americas in 1492, to 18 million in Henry F Dobyns's Their Number Become Thinned (1983). Henry F Dobyns' work, being the highest single point estimate by far within the realm of professional academic research on the topic, has been criticized for being "politically motivated". Perhaps Dobyns' most vehement critic is David Henige, a bibliographer of Africana at the University of Wisconsin, whose Numbers From Nowhere (1998) is described as "a landmark in the literature of demographic fulmination." "Suspect in 1966, it is no less suspect nowadays," Henige wrote of Dobyns's work. "If anything, it is worse."
After the thirteen colonies revolted against Great Britain and established the United States, President George Washington and Henry Knox conceived of the idea of "civilizing" Native Americans in preparation for assimilation as U.S. citizens. Assimilation (whether voluntary, as with the Choctaw, or forced) became a consistent policy through American administrations. During the 19th century, the ideology of manifest destiny became integral to the American nationalist movement. Expansion of European-American populations to the west after the American Revolution resulted in increasing pressure on Native American lands, warfare between the groups, and rising tensions. In 1830, the U.S. Congress passed the Indian Removal Act, authorizing the government to relocate Native Americans from their homelands within established states to lands west of the Mississippi River, accommodating European-American expansion. This resulted in the ethnic cleansing of many tribes, with the brutal, forced marches coming to be known as The Trail of Tears.
As American expansion reached into the West, settler and miner migrants came into increasing conflict with the Great Basin, Great Plains, and other Western tribes. These were complex nomadic cultures based on (introduced) horse culture and seasonal bison hunting. They carried out resistance against United States incursion in the decades after the end of the Civil War and the completion of the Transcontinental Railroad in a series of Indian Wars, which were frequent up until the 1890s and continued into the 20th century. Over time, the United States forced a series of treaties and land cessions by the tribes and established reservations for them in many western states. U.S. Indian agents encouraged Native Americans to adopt European-style farming and similar pursuits, but European-American agricultural technology of the time was inadequate for the often dry reservation lands, leading to mass starvation. In 1924, Native Americans who were not already U.S. citizens were granted citizenship by Congress.
Contemporary Native Americans have a unique relationship with the United States because they may be members of nations, tribes, or bands with sovereignty and treaty rights. Cultural activism since the late 1960s has increased political participation and led to an expansion of efforts to teach and preserve indigenous languages for younger generations and to establish a greater cultural infrastructure: Native Americans have founded independent newspapers and online media, recently including First Nations Experience, the first Native American television channel; established Native American studies programs, tribal schools, and universities, and museums and language programs; and have increasingly been published as authors in numerous genres.
The terms used to refer to Native Americans have at times been controversial. The ways Native Americans refer to themselves vary by region and generation, with many older Native Americans self-identifying as "Indians" or "American Indians", while younger Native Americans often identify as "Indigenous" or "Aboriginal". The term "Native American" has not traditionally included Native Hawaiians or certain Alaskan Natives, such as Aleut, Yup'ik, or Inuit peoples. By comparison, the indigenous peoples of Canada are generally known as First Nations.