(1806 - 1848).
From the time of European settlement of North America in the seventeenth century, the western frontier was the initial geographical impediment to expansion, the crest of the Appalachian Mountains. While the eastern seaboard was being tamed, little concern and speculation was given the area over these mountains. After independence, migration began en masse over the Appalachians and the western frontier moved further west to the next great geographical boundary. After the Revolutionary War, the conflict among European powers over the vast American continent and its riches gave way to the new nation of the United States. With peace came an impetus for westward expansion, as veterans returned to areas seen during the war, and land hungry settlers traveled to newly available lands in New York and across the Appalachians.
At the beginning of the 19th century, the American frontier was approximately along the Mississippi River, which bisects the continental United States north-to-south from just west of the Great Lakes to the delta near New Orleans. St. Louis, Missouri was the largest town on the frontier, the gateway for travel westward, and a principal trading center for Mississippi River traffic and inland commerce.
The new nation began to exercise some power in domestic and foreign affairs. The British had been driven out of the East after the American Revolutionary War but remained in Canada and threatened to expand into the Northwest. The French had left the Ohio Valley but still owned the Louisiana Territory from the Mississippi River west to the Rockies, including the strategic port of New Orleans. Spain's dominion (New Spain) included Florida and the territories from present-day Texas to California along the southern tier and up to what later would be Utah and Colorado.