The U.S. Monroe Doctrine, established in 1823, aimed to prevent European colonial powers from interfering in the affairs of the Americas. President James Monroe asserted that any attempt by foreign nations to colonize or intervene in the Western Hemisphere would be viewed as acts of aggression, prompting U.S. intervention. This doctrine underscored a shift in U.S. foreign policy toward a more assertive role in regional matters and laid the groundwork for future American actions in Latin America. Overall, it signaled the U.S.'s intention to protect its own interests and influence in the Americas, fostering a sense of American nationalism and independence.