Over the first six decades of the nineteenth century, multiple political, social, and economic factors drove American territorial expansion.
Before the Revolution, Great Britain attempted to keep colonists from moving across the Appalachian Mountains and into the frontier, where they might incite costly conflicts with Native Americans and grow still more independent. This repression was one several colonial grievances that led to the American Revolution. After the war, thousands of Americans poured into the Ohio River Valley and other areas, where they seized and then farmed lands long controlled by native peoples.
This Anglo American expansion quickened from 1800 to 1860. The Louisiana Purchase more than doubled the young nation’s size, and a treaty with Mexico added a vast expanse of land to the southwest. Thousands of ambitious planters, small farmers, traders and entrepreneurs, miners, and others sought their fortunes in these lands.