Westward Expansion was the process of America's expansion to the west. It began with the Louisiana Purchase, followed by Lewis and Clark's expedition west. The Oregon Trail story was part of it, too. The 49er's in the California gold rush were also part of westward expansion. The pony express, a mailing system to the west through ponies were also part of it. It came to an end with the building of the transcontinental railroad.
They were important because they were not controlled by the government or the church. Therefore they were free to explore in scientific experiments as much as they wanted without these controls.
