How did territorial expansion the united states to grow economically

Victory over the British in the War of 1812 confirmed the independence of the new American republic, promoting a sense of national self-confidence and pride. It also encouraged expansionism: In the decades prior to the Civil War, the nation grew exponentially in size, as restless white Americans pushed westward across the Appalachians and the Mississippi, and on to the Pacific. These white settlers were driven by hunger for land and the ideology of "Manifest Destiny." They forced the removal of many Native American nations from the Southeast and Northwest. They acquired a large part of Mexico through the Mexican-American War, and they engaged in racial encounters with Native Americans, Mexicans, Chinese immigrants, and others in the West. 

With territorial expansion came economic development that fed growing regional tensions. In the northern states, economic development ushered in the early stages of industrialization, a transportation revolution, and the creation of a market system. The North's cities flourished on a rising tide of immigration, and its newly opened territories were cultivated by growing numbers of family farms. The South followed a dramatically different course, however, staking its expansion on the cotton economy and the growth of slavery. While white Southerners fiercely defended this exploitive economic and social system, millions of African American slaves struggled to shape their own lives through family, religion, and resistance. 

The rapid expansion of American society in the first half of the 19th century put new demands on the political system. For the first time, interest-group politics came to the fore, marking the advent of modern politics in America. Some groups were not yet part of the political system: efforts to secure women's suffrage failed, and free African Americans remained disenfranchised in many parts of the North. However, this period also saw one of the greatest bursts of reformism in American history. This reform was both an attempt to complete the unfinished agendas of the revolutionary period and an effort to solve the problems posed by the rise of factory labor and rapid urbanization. It laid the groundwork for social movements--such as the civil rights and feminist movements--that continue to be significant forces in American society today.