What key principle was established by the Monroe Doctrine?

The Monroe Doctrine established the key principle of excluding European interventions in the Americas. This doctrine, articulated by President James Monroe in 1823, signaled a clear stance against European colonialism in the Western Hemisphere. It asserted that any attempt by European powers to colonize or interfere with states in North or South America would be viewed as acts of aggression, warranting U.S. intervention. This policy aimed to protect the newly independent nations in Latin America from European re-colonization and to assert a sphere of influence for the United States in the Americas.

By emphasizing the importance of non-interference, the Monroe Doctrine became a cornerstone of American foreign policy and laid the groundwork for the U.S. role as a dominant power in the western hemisphere, advocating for the sovereignty of nations in the Americas against European dominance.