Expansionists were people who wanted to extend the boundaries of the newly formed United States nation in all directions, even if this meant buying or seizing territory from Spain (in the Southwest and Florida), France (the Louisiana Territory along the Mississippi River), and Great Britain (the Northwest Territories of Canada). Not long after the colonists won the American Revolution (1776–83; the conflict in which the American colonies won independence from Great Britain), founding the United States of America, a nationalistic (patriotic) spirit emerged in the hearts of many citizens of the new country. A growing population, made possible by an influx of immigrants (people who permanently settle in a foreign country) and improved farming methods, fueled expansionist ideas. Built upon the expansionist idea, the concept of Manifest Destiny (the belief that the United States had a God-given right to expand its territory) emerged by the 1840s. As settlers moved westward, the U.S. government forced Native Americans off their tribal lands to make room for the settlers. In the two decades between 1840 and 1860 alone, the population of the United States more than doubled, increasing from just over 17,000,000 to more than 38,000,000. At mid-century, half of the U.S. population lived outside of the original thirteen colonies. By 1853, the United States owned all the territory that today makes up the contiguous states.
Further Information: Foote, Timothy. "1846: The Way We Were—and the Way We Went." Smithsonian. April, 1996, pp. 38-49; "Manifest Destiny." Encyclopedia Britannica. [Online] Available http://www.britannica.com/bcom/eb/article/7/0,5716,51777+1+50542,00.html, October 22, 2000; Philippine-American War Centennial Initiative. History of U.S. Territorial Acquisitions. [Online] Available http://www.phil-am-war.org/territorial.htm, October 22, 2000.