What reason would people give at the end of the 1800s for why the united states should expand outside the continent?

1 reason may be the idea of Manifest Destiny
Another reason may be that the price for some land was cheap, for example when we bought the Louisiana territory for a small price from France
There were also many opportunities for more jobs, and more money
The idea of being a westward person was ideal and somewhat “fantasized”
Also, once they had purchased, the discovery of gold lured many people

Social darwinism refers to the the theory that people who succeed in our economic system will one day out compete those who fail. one day the rich will out succeed the poor so we'll that there will eventually be no more poor