Which doctrine warned European powers against further colonization in the Americas?

The Monroe Doctrine is significant because it established a clear policy that opposed European colonialism in the Americas. Instituted in 1823 during President James Monroe's administration, the doctrine declared that any further attempts by European nations to colonize or interfere in the affairs of countries in the Western Hemisphere would be viewed as acts of aggression, requiring U.S. intervention.

This doctrine was aimed at ensuring the sovereignty of nations in the Americas and preventing the resurgence of European colonial influences, particularly in light of the decolonization movements spreading through Latin America at that time. It was a pivotal moment in shaping U.S. foreign policy, emphasizing a stance of protection and dominance over the Western Hemisphere.

The other options reference different historical contexts and policies. The Truman Doctrine was primarily about containing communism, the Eisenhower Doctrine focused on the Middle East, and the Roosevelt Corollary expanded on the Monroe Doctrine by asserting the U.S. right to intervene in Latin America to maintain stability. These distinctions help clarify why the Monroe Doctrine specifically addresses European colonization in the Americas.