In December 1823, US President James Monroe articulated what would become one of the most enduring pillars of American foreign policy. The Monroe Doctrine declared the Western Hemisphere off-limits to further European colonisation or interference, positioning the United States as the guardian of the New World. Though initially dismissed by European powers, the doctrine gradually evolved into a foundational claim of hemispheric authority. It framed the Americas not merely as a geographical space, but as a strategic domain under American supervision.