Westward expansion was a key theme of nineteenth-century America. In 1803, President Thomas Jefferson bought the Louisiana Purchase from France. He hoped that small farmers would move to the newly acquired lands and settle on small farms. Western settlement took almost the entire century.

Manifest Destiny was the idea that America was destined to settle all territory between the Mississippi River and the Pacific Ocean. The western frontier was an opportunity for Americans who sought new lives. In 1848, the US took huge tracts of land from Mexico after winning the Mexican-American War (1846–48). This territory practically completed the boundaries of the continental US as we know it.

The acquisition of vast territory led to heated disputes between North and South. The North wanted the new territories to be free, but the South wanted them to be slave states. The arguments became increasing bitter during the 1850s, and this slowed settlement. After the end of the Civil War in 1865, the pace of settlement quickened. Transcontinental railroads were built. Indian tribes were subdued. Cowboys roamed the West.

Historian Frederick Jackson Turner argued that the frontier was an essential component of the nation's character. By the late nineteenth century, that frontier was gone.

Westward expansion dramatically shaped the face of our nation in many ways.  Obviously the size of our nation grew tremendously beginning with the Treaty of Paris (1783) that defined our nation as everything east of the Mississippi River.  The Louisiana Purchase (1803) doubled the size of our country, and the Texas Annexation/ Mexican Cession practically doubled it again.

As a result of this dramatic increase in land immigrants and slaves by the millions came to America to work the land, both voluntarily and involuntarily.  As new people came to America, a plan had to be put into place for the orderly expansion of or nation.  The Northwest Ordinance servied that purpose well, and new states began to form.

The addition of new states exacerbated the problem of slavery in the United States, as the uneasy balance of power of our nation was threated by the addition of new states and whether or not the would be a slave state.  In many ways, westward expansion could be considered a key cause of the Civil War, though it is often overlooked.

Regarding industry, new industries popped up to service these new lands with the greatest being transportation.  Trains and steam engines helped facilitate travel and spearheaded new industries to build the necessary machines and employed thousands in the construction of infrastructure... a budding new industry in of itself.  Obviously the discovery of gold in California in the 1840s drew millions of people to the west coast in search of riches, and service industries blossomed to service those people.  Additionally, when the lure of fast money didn't pan out, those people sought out work or land ownership instead.