By being hard to do the work because it does get hot out when doing that kind of job
They passed the Espionage and Sedition Acts which allowed the government to arrest and fine anyone speaking out against the war.
Lewis and Clark expedition
Talk about the three G's; Gold, Glory, and God.
Also, at the time, land was equal to power. The more land you had, the richer you were. This is a social and political reason, as well as economic.
Hope this helps you. Ask any questions if you need to!