Final answer:
Native American nations faced conflict, forced relocations, and assimilation policies in reaction to the United States' expansion. They experienced a loss of land and sovereignty, despite attempts at resistance and negotiation, culminating in the institution of the reservation system.
Step-by-step explanation:
The reaction of Native American nations to the rapid growth of the United States was complex and varied. The expansion of American settlers into Native lands often resulted in conflict, due to the desire of the settlers and the U.S. government to claim land inhabited by indigenous peoples. This direct competition for land, combined with cultural differences and misunderstandings, led to a series of brutal clashes and wars, mostly resulting in tragic outcomes for the Native Americans. Many tribes attempted to resist through military means, but others sought to adapt or negotiate under difficult circumstances, facing forced relocations such as the Trail of Tears and the reservation system.
The imposition of American laws and policies further attempted to assimilate Native American tribes into American society, often at the expense of their cultures and traditional ways of life. These policies included enforcing individual land ownership, western education, Christianity, English language, and American capitalist values. Native American sovereignty was recognized to some extent through the Marshall Court trilogy, which established them as domestic dependent nations under the protection of the federal government, yet this did little to prevent the overall decline of Native American autonomy and territory.