Who were the first immigrant group to make an impact on the culture and society of the western United States?

Mexican-Americans

Explanation:

Mexican - Americans were the first immigrant group who entered in the West and introduced their culture and society that impacted the local natives living there. For the first time, in 1519, after the Spanish arrived in the Americas, they began to build farmland and ranches to raise livestock. Horses imported from Spain and Vaqueros (cowboys) were introduced in the area to look after the cattle.