Manifest Destiny

Manifest Destiny was the belief widely held by Americans in the 19th century that the United States was destined to expand across the continent. The concept, born out of "a sense of mission to redeem the Old World", was enabled by "the potentialities of a new earth for building a new heaven". The phrase itself meant many different things to many different people. The unity of the definitions ended at "expansion, prearranged by Heaven". Mid-19th-century Democrats would use it to explain the need for expansion beyond the Louisiana Territory.

Manifest destiny provided the dogma and tone for the largest acquisition of U.S. territory. It was used by Democrats in the 1840s to justify the war with Mexico and it was also used to acquire portions of Oregon from the British Empire. But Manifest Destiny always limped along because of its internal limitations and the issue of slavery, says Merk, and never became a national priority. By 1843 John Quincy Adams, a major supporter, had changed his mind and repudiated Manifest Destiny because it meant the expansion of slavery in Texas.

The legacy is a complex one. The belief in an American mission to promote and defend democracy throughout the world, as expounded by Abraham Lincoln and later by Woodrow Wilson and George W. Bush, continues to have an influence on American political ideology.