The Monroe Doctrine was established in 1823 by President James Monroe as a cornerstone of U.S. foreign policy. It aimed to prevent European nations from colonizing or interfering in the affairs of countries in the Americas, declaring such actions as acts of aggression that would necessitate U.S. intervention. This policy was a response to the growing concern over European imperial ambitions in Latin America and specifically aimed to deter any recolonization efforts following the independence movements in former Spanish colonies. By positioning the United States as a protector of the Western Hemisphere, the Monroe Doctrine sought to limit European influence in the region, a crucial aspect of U.S. history in the 19th century.