The Monroe Doctrine, established in 1823, articulated a principle of American foreign policy aimed at opposing European colonialism in the Americas. It asserted that any intervention by external powers in the politics of the Americas would be viewed as an act of aggression requiring U.S. intervention. The doctrine aimed to protect newly independent Latin American nations from European interference and sought to establish the Western Hemisphere as a sphere of influence for the United States. It laid the groundwork for future U.S. foreign policy in the region, asserting American leadership and fostering nationalism in the Americas.