Why did some americans oppose u. s expansion?

While Americans in general wanted the country to expand, not all Americans agreed with this sentiment. Many Americans did not believe that the country should expand. They gave several reasons for this. Some Americans believed that expansion was problematic for Native Americans. They believed that Native Americans deserved to continue living in their ancestral areas. Another  reason was the fact that many people believed that in order for America to expand, other nations needed to suffer. This was the case with countries such as Mexico.

i don't know why don't you google it?