Even though the U. S. government bought a substantial portion of Indian land, why is it still seen as an unfair Act?

Federal relations with Indian tribes were centered on trading, wars, and treaty making. In an 1831 decision, the Supreme Court described tribes as "domestic dependent nations" that had broad latitude to create their own laws within tribal areas. In an 1832 decision, the Court ruled that only the federal government could regulate Indian affairs, not state governments.  The federal government signed more than 400 Indian treaties during this period, with tribes usually receiving various payments and benefits in return for ceding land. State governments, settlers, and businesses pressured the federal government to seize Indian lands for their own use, and more than 100,000 Indians from the Southeast were pushed off of their lands and moved to reservations west of the Mississippi River.

Explanation:

it affected it because the kingdoms (with trade) slowly got richer and richer.