The purpose of the Monroe Doctrine in U.S. history was to assert that the Americas should be free from European colonial influence. Declared by President James Monroe in 1823, the doctrine warned European powers against further colonization or interference in the Western Hemisphere. It emphasized the U.S. commitment to defending the sovereignty of nations in North and South America. The doctrine became a cornerstone of American foreign policy, signifying an expansionist view and leading to the U.S.'s role as a regional power while shaping relations with both European nations and neighboring countries.