After the colonies revolted against Great Britain and established the United States 
of America, President George Washington and Henry Knox conceived of the idea of 
"civilizing" Native Americans in preparation for United States citizenship. 
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 after the American Revolution resulted in increasing 
pressure on Native American lands, warfare between the groups, and rising tensions. 
In 1830, the US Congress passed the Indian Removal Act, authorizing the government 
to relocate most Native Americans of the Deep South east of the Mississippi River from 
their homelands to accommodate European-American expansion from the United States. 
Government officials thought that by decreasing the conflict between the groups, they 
could also help the Indians survive. Remnant groups have descendants living throughout 
the South. They have organized and been recognized as tribes since the late 20th 
century by several states and, in some cases, by the federal government.

The first European Americans encountered western tribes as fur traders. As United 
States expansion reached into the American West, settler and miner migrants came 
into increasing conflict with the Great Plains tribes. These were complex nomadic 
cultures based on using horses and traveling seasonally to hunt bison. They carried 
out strong resistance to American incursions in the decades after the American Civil 
War, in a series of "Indian Wars", which were frequent up until the 1890s. 
The coming of the transcontinental railroad increased pressures on the western tribes. 

Over time, the US forced a series of treaties 
and land cessions by the tribes, and established reservations for them 
in many western states. US agents encouraged Native Americans to adopt 
European-style farming and similar pursuits, but the lands were often too poor to 
support such uses.

Contemporary Native Americans today have a unique relationship with the United 
States because they may be members of nations, tribes, or bands of Native Americans 
who have sovereignty or independence from the government of the United States. 
Their societies and cultures flourish within a larger population of descendants of 
immigrants (both voluntary and slave): African, Asian, Middle Eastern, and European 
peoples. Native Americans who were not already U.S. citizens were granted 
citizenship in 1924 by the Congress of the United States.