The main reason for the U.S.-imposed Monroe Doctrine, introduced in 1823, was to prevent European intervention in the affairs of the Americas. President James Monroe articulated this policy during his annual address to Congress, asserting that the Western Hemisphere was no longer open to colonization or interference by European powers. The doctrine aimed to protect newly independent Latin American nations and to assert U.S. influence in the region. It became a cornerstone of American foreign policy, reflecting a desire to maintain autonomy in the Western Hemisphere and to foster a sense of nationalism and solidarity among American states.