Expansionism in the 19th and early 20th century U.S. was not a continuation of past American Expansionism. Throughout American history, prime motives for geographical and political expansion have been in support of U.S. economy. As the country grew, many other issues became important in the shaping of American expansionism. Slavery and investment of capital were major forces behind these issues. All these events involved economic, societal, and political expansion.
Colonial expansion was meant to facilitate growth in population and build economic base to support that population. This can be seen in the purpose of the seven years war and war of 1812. Britain and the colonials intended to remove the French from the Americas in order to open up the vast area of land under their control in the west. Between and after these wars, expansion into these newly acquired lands was better made possible with the Northwest Ordinance and removal of Indians.
By first attempting to move Indians east of the Mississippi River, land around large rivers would then be open for farming. This was the purpose of the Northwest Ordinance. It was meant to open up the Ohio River Valley to settlers, most specifically farmers, to increase the production of raw goods that were needed to support America's growing population. With the eventual purchase of the Louisiana Territory, rivers such as the Mississippi and Ohio became crucial to the development of trade and economy during this period of History.
During the Mid 19th century, expansionist philosophy began to change. Important societal issues, such as slavery and religion, became a resounding force in every decision. In the 1830s and `840s, the westward movement of people left the valley of the Mississippi behind, stretching far into the west, all the way to the Pacific. A new philosophy, known...