The Fur trade soon led to the sighting of good farm lands in the mid-west, which prompted many to move there for cheap land and good farmland. After that, the discovery of gold prompted even more to go towards the west in a attempt to strike it rich
hope this helps
There are several ways in which the U.S. increased western settlement in the 1800's, but by far the most important action was the creation of the Homestead Act.