The period from the Mexican-American War to World War I saw the rise of American imperialism. The country slowly was making its name known across the globe, and was in the throes of an Industrial Revolution of its own. Its territory now stretched “from sea to shining sea”, and thus it looked across the Pacific Ocean and the Atlantic Ocean in search of territories it could call as its own and from which vast natural resources could be extracted to aid in the Industrial Revolution thereat. Perhaps the first theoretical underpinning which eventually led to US imperialism is the Monroe Doctrine. It formed the basis of foreign policy in 1823 which declared that any intervention or presence of any European power in the Americas was to be viewed by the United States as an act of violence or aggression that would necessitate US intervention or presence. This doctrine came at a time when many Latin American nations were fighting for their own independence from Spain (Herring, 2008, 153-155).
Also, at this time, the consciousness of the American public was drawn to the notion of ‘Manifest Destiny’. This concept meant that the country was destined (even divinely, as others posited), to expand its territories outward across the North American continent and even beyond the Atlantic and the Pacific Oceans. The term was first coined by John O’Sullivan, a newspaperman, in 1845 to derive support for the annexation of Texas. Afterwards, the term was also used to justify the westward expansion of the nation into the Great Plains and the Pacific side of the country. Thereafter, it was used again to justify expansion outside the now wider territory of the nation (Greenberg, 2005, 28-30). Manifest Destiny proclaimed that the United States would bring the message of democracy to their new ‘territories’. Outside of the US mainland, expansion began with the purchase of Alaska, the annexation of Hawaii and of Puerto Rico, and the purchase of the US Virgin Islands from Denmark. That Manifest Destiny also had a racial component to it is reflected in the fate of the Native Americans at this time. The Homestead Act of 1862 caused westward migration, as land was given to them literally for free, and with the signing of the Treaty of Paris in 1898, the United States had sovereignty over the Philippines, Cuba, Puerto Rico and Guam. These islands were treated as colonies, which further supported the country’s desire for hegemony and a stronger position on the world stage.
Greenberg, Amy. (2005). Manifest Manhood and the Antebellum American Empire. New York: Cambridge University Press.
Herring, George. (2008). From Colony to Superpower: US Foreign Relations Since 1776. New York: Oxford University Press.