What is Manifest Destiny?
In early nineteenth century America, the quest for lands in the West became an obsession. The allure of the frontier was enticing, and the obstacles that had been in the way of settlers moving west had been removed. The Native Americans were continually pushed out of the way and dislodged from their lands. In 1783, the British were defeated during the American Revolution. In 1803, the French sold their rights to the land that became known as the Louisiana Purchase to the United States.
From this point, there was seemingly nothing to stop this westward expansion. It became the ideal in America during this era, and the slogan “Manifest Destiny” encapsulated all the fine points of, and justification for, the move westward for thousands of people.
The words were first heard in America, in 1845. They were first published in an article found in the newspaper, The United States and Democratic Review. The title of the article was “Annexation,” and it advocated for the annexation of the Republic of Texas, to the United States, which would add more territory for settlement, as well as business pursuits, to the growing country. According to the article, it was “our manifest destiny to overspread the continent allotted by Providence for the free development of our yearly multiplying millions.” 
This phrase quickly became the identifiable slogan that defined the idea of westward expansion in America. Proponents of this concept were pro-annexation, and pro-expansion. This idea helped to justify a war with Mexico, in 1846, which resulted in gaining the entire southwestern portion of the present day United States.