A Manifest Destiny was a term used in the 1840s to justify the United States' westward expansion into such areas as Texas, Oregon, and California. There was a widely held underlying belief that Americans, the "chosen people," had a divinely inspired mission to spread the fruits of their democracy to the less fortunate (usually meaning Native Americans and other non-Europeans).
The idea of an almost religious Manifest Destiny was a common staple in the speeches and newspaper articles of the time. Most of the exponents of expansion were Democrats, but some Whigs (and later Republicans) were also supporters.
Manifest Destiny was later applied to American interests in the Caribbean and the Pacific.