Manifest Destiny was a concept which heavily influenced American policy in the 1800s. The idea was the driving force behind the rapid expansion of America into the West from the East, and it was heavily promoted in newspapers, posters, and through other mediums. While Manifest Destiny was not itself an official government policy, it led to the passage of legislation such as the Homestead Act, which encouraged Westward colonization and territorial acquisition. It also played an important role in American thought.

The term was first used in 1845 by John O'Sullivan, an American newspaper editor who was writing about the proposed annexation of Texas. O'Sullivan stated that it was America's “manifest destiny to overspread the continent.” The editorial suggested that through expansion, the United States could become a recognized political and social superpower. America had, in fact, O'Sullivan argued, been uniquely chosen for the task of expanding Westward, driving out the wilderness and establishing civilization.

The Westward expansion of the United States did not, of course, begin with Manifest Destiny. The Louisiana Purchase of 1803, in which 23% of the existing territory of the United States was acquired, was probably the first major step. The government saw the appeal in acquiring more land, as well as the potential political power which large tracts of land could confer upon the young nation. As a result, a policy pursuing aggressive expansion was actively pursued. The idea of Manifest Destiny was merely a component, and one which captured the popular imagination.

O'Sullivan's Manifest Destiny editorial added fuel to the fire with a catchy phrase. Numerous government campaigns painted the allures of the West for prospective settlers, and promoted programs which could help people acquire and hold land in the West. With the discovery of gold and other valuable minerals, a tide of Easterners started to pour into the West, supported by their belief in their right and duty to expand.

The idea of Manifest Destiny was also behind American political actions overseas. Although the term ceased to be used in a political context in the early twentieth century, the far-reaching impact of Manifest Destiny was clear. A section of the Manifest Destiny editorial reminded Americans that they were uniquely positioned to spread democracy throughout the world, and this concept clearly played a role in twentieth century American foreign policy. Many historians use the term “Manifest Destiny” to refer to the period in American history which was marked by rapid expansion “from sea to shining sea” through annexation of the Western half of the continent.