Evaluate the effects of post–Civil War expansion on Native Americans.

Post–Civil War expansion of the United States had a largely negative effect on Native Americans, a trend which had continued since the earliest arrival of Europeans in the Americas. Thriving Native American civilizations in the West faced threat and destruction from post–Civil War settlement, in much the way Native American societies in the East faced destruction in earlier centuries.
The development of railroads across the United States made the prospect of moving west even more appealing to many Americans. Whether they were aiming to search for gold, develop agriculture, or escape life in the east, huge numbers of Americans moved west. As American settlers claimed land, they came into conflict with Native Americans already living in the West.
One solution to the conflict with the Native Americans that was developed by the US government was the intentional killing of the bison population. It was understood that the bison were an essential source of life for Native Americans, as they hunted bison for food, clothing, and other needs. In some cases, American troops were ordered to kill as many bison as they could in order to defeat the Native Americans. This strategy devastated not only the bison population, which at one point was nearly extinct, but also the Native Americans who were dependent upon them.
As more settlers headed west and the US military moved to support them, Native American resistance was largely defeated. By the late 1880s, most Native Americans had been moved onto reservations after the US government approved the Reservation System. Reservations were often located on pieces of land which were deemed to have little value to settlers. The Reservation System allowed Native Americans to maintain some of their land (unless they belonged to one of the tribes that were forced off of their homeland into an entirely new place), some level of autonomy, and an ability to retain aspects of their culture, but it did not provide them with much opportunity for economic success or self-sufficiency.
Through the Reservation System, the US government promised to supply food, goods, and protection for the Native Americans on their reservations. These promises, however, were not well fulfilled. In many cases, Native tribes came into conflict with each other over the scarce resources available. Native Americans who refused to agree to the reservation plans were viewed as enemies and a nuisance that needed to be removed. The final resistance to white settlement in the West is considered to have happened at the Battle of Wounded Knee, in 1890. With a victory for the American military, it was determined that the West would be peopled by white settlers, and Native Americans would lose their ancestral homelands, suffer a great decline in quality of life, and be forced onto reservations.
It can safely be said that the impact of post–Civil War expansion of the United States had a very negative impact on Native Americans living in the West. It can also be argued that many western Native American cultures have still not recovered, and may never fully recover, from white American expansion.
http://www.loc.gov/teachers/classroommaterials/presentationsandactivities/presentations/timeline/riseind/west/

https://www.history.com/topics/native-american-history/american-indian-wars

https://www.pbs.org/buffalowar/buffalo.html