is land they took from others.
In the case of the Sioux, you are probably wrong. The upper Great Plains were largely uninhabitable to Indians peoples; it is dry, barren and prone to temperature extremes. Thus, both farming and even hunting-and-gathering are impractical. Contrary to their legends, the Sioux almost certainly came from Western New York and the Allegheny region. As white man encroached, the Sioux found that, with horses, previously uninhabitable areas to their west offered a new way of life, and moved West rather than fighting for the lands they were more familiar with. With the advantages they gained from white men, they were able to live in this new land as well as they had lived in their ancient homelands.
MOst of the time, I defend the white man's taking of "Indian lands" by pointing out that Indians had never really possessed the lands in the first place. The Indian population density was at its greatest about 1 person per square mile in the U.S. We were moving into largely empty land.
However, the means we used of doing so were unenlightened, un-Christian, and sometimes simply vicious. While areas of the East coast now team with population densities in the tens of thousands, South Dakota is still largely uninhabited. The abuse of the Sioux was entirely unnecessary and unjust.