American settlers began moving westward in the 1800s, pushed by beliefs like Manifest Destiny that the United States should expand from coast to coast. Pioneers moved beyond the Appalachian Mountains in search of new land and opportunities. In 1803, President Thomas Jefferson negotiated the Louisiana Purchase, doubling the size of the young nation by acquiring land west of the Mississippi River from France for $12 million. This opened up vast new territories for further western expansion.