Manifest Destiny
Now that the spirit of nationalism was sweeping the nation and the grow population needed territory. The Jacksonian Era fueled an optimistic outlook for the nation. The new territory recently explored, the Louisiana Purchase, the Americans were heading west. The fur trade was a very important reason for the sudden growth in population. The new fur economy challenged the Europeans fur trade for the first time. The gold recently discovered created a gigantic spike in population with all the citizens looking the hit the jackpot of gold and become rich. This becomes one of the main reasons for the large population numbers on the west coast. Also a sudden religious fever spike in the nation that believed god had blessed the nations new growth to the west. Along the was many Christian missionaries went to Native American tribes and christianized many of the Native Americans. Expanding the United States borders was very much a cultural war as anything else. The desire for southerners to get their hands on the newly expand land to continue cotton growing and slavery was enormous. Although North of the Mason-Dixion line citizens were worried about adding more slave states.
Sources
http://www.history.com/topics/manifest-destiny
http://www.pbs.org/kera/usmexicanwar/prelude/manifest_destiny_overview.html
http://www.pbs.org/kera/usmexicanwar/prelude/manifest_destiny_overview.html