Answer/Explanation
The US sought to defend its eastern border from attack and drive Spain from power in the Americas.
By 1860 almost half of the American people lived west of the Appalachian Mountains. In the 19th-century movement of settlers into the American West, was initiated with the Louisiana Purchase and Lewis and Clark´s expedition. I was also triggered by the California Gold Rush, the Oregon Trail and "manifest destiny." Manifest destiny was the believe that Americans were meant to expand across all of North America.
