What doctrine justified American intervention in foreign territories during the age of imperialism?

The Monroe Doctrine is the correct choice because it established a foundational principle for American foreign policy in the Western Hemisphere. Formulated in 1823, the doctrine declared that any European intervention in the affairs of nations in the Americas would be viewed as an act of aggression, prompting U.S. intervention. This principle evolved over time and was instrumental in justifying American actions in Latin America, where the U.S. aimed to limit European influence and assert its own dominance in the region.

While the other doctrines have played significant roles in American foreign policy, they do so in different contexts. The Roosevelt Corollary, for instance, built upon the Monroe Doctrine by asserting the right of the United States to intervene in Latin American countries to maintain stability, specifically to prevent European powers from reasserting control. The Truman Doctrine addressed the threat of communism post-World War II, focusing on containing the Soviet influence rather than imperialism per se. Lastly, Wilsonian Idealism promoted democracy and self-determination but was less about intervention for imperialistic reasons and more about spreading democratic values. Each of these doctrines reflects different historical contexts and motivations, but the Monroe Doctrine is key to understanding the rationale behind early American imperialism.