Which term describes americans who were opposed to immigrants?

Nativists is the correct term to describe Americas who opposed immigration.

Explanation:

Nativism is a nationalistic fundamental ideology that says that a certain country's wealth and goods have to be distributed only or the natives. It is a protective retrograde ideology that goes against multiculturalism and diversity. It is very often fundamental in birthrights and encourages people to perform serialism and indirect discrimination. It is not only practiced in the united states and is based on the fear of being displaced by other groups of the population.