Unit question: How was the idea of "manifest destiny" used to justify westward expansion?

Manifest destiny is the phrase used to describe Americans belief that they had a "God-given" right to "overspread" the continent, "from sea to shining sea." The westward expansion of the United States carried with it many of the positive things about America into the western territories, like it's revolutionary principles of government and unique Constitution, however the acquisition (to acquire, gain) of these territories came at the expense of Native American tribes already living there. In some cases, like the Texas territory, it's secession and annexation came at the expense of a foreign country. The Frontier, or the open-range, had a mythology as being a wilderness to be tamed by cowboys, pioneers, and settlers. The cession of lands from Spain (Florida) and Mexico paved the way for the developing industrial nation to innovate existing technologies to pave the way for the modern America we have today. These new technological innovations remade and revolutionized agriculture in the Southern and Western regions, as well as transportation and communication in the North and Western regions (mostly in the North) that led to a manufacturing boom. Along with religious revivals such as the Second Great Awakening, a free enterprise system (economy) was built that would start to question the morality and profitability of slavery. Sectionalism, the word given to this struggle, would create conflict within the (relatively) New Republic over the expansion of slavery and imperialism. Eventually these moral/ethical issues would lead to a period of drastic and radical reform, but for units 4, 5, and 6 it would be a nasty and messy battle for equality for not only slaves and freedmen, but immigrants as well. These units are the foundation for the world we live in today.

Unit Question: What factors contributed to economic growth in the United States in the 19th century?