The Monroe Doctrine was articulated by President James Monroe in his 1823 address to Congress, declaring that the Western Hemisphere was closed to further European colonization and that any European intervention in the Americas would be considered a threat to U.S. security. It was not codified as law but became a foundational principle of U.S. hemispheric policy. The doctrine has been invoked, extended, and reinterpreted by presidents across two centuries — from Theodore Roosevelt's 1904 "Roosevelt Corollary" (which claimed the U.S. right to intervene in Latin American affairs) to Reagan's use of the doctrine to justify Central American interventions in the 1980s. Trump's Shield of the Americas summit represents the latest iteration: a "Trump Corollary" framing U.S. military authority over the hemisphere not as a defensive response to external threats but as an active project of regional security leadership centered on American military power and ideological alignment.