There were several different factors that caused the US to become a part of the imperialist movement, including:
1) Industrialization- The invention of technologies that allowed for the mass production of goods allowed businesses to make more of their products than ever before. Due to their increased ability to make large sums of goods, these individuals wanted the US to expand their global influence so that they may have new consumers to sell their products too.
2) Social Darwinism- This idea revolves around the concept of the "survival of the fittest." Many Americans felt that the US was a superior society that should spread its ideas and influence in order to help less civilized countries/territories.
The Indian reservation system established tracts of land called reservations for Native Americans to live on as white settlers took over their land.
<span>(d) passing the Stamp Act
The colonists did not believe that they should be taxed more heavily, and when they had to pay more than before for stamps, they decided to boycott it
hope this helps</span>
Answer: Well, according the the all-knowing Googs:
"Immigration to the U.S. in the Late 1800s. Between 1870 and 1900, the largest number of immigrants continued to come from northern and western Europe including Great Britain, Ireland, and Scandinavia. But "new" immigrants from southern and eastern Europe were becoming one of the most important forces in American life."
However!! Uh, There is no 'however', but I hope this lazily-obtained answer helps you, and if it does not, then comment and I will scour the internet for the answer in which. you. seek.