What policy describes the U.S. stance of opposing European colonialism in the Americas?

The Monroe Doctrine is the policy that articulates the United States' stance of opposing European colonialism in the Americas. Announced in 1823 by President James Monroe, this policy declared that any further attempts by European nations to colonize or interfere with states in North or South America would be viewed as acts of aggression against the United States, prompting a strong response. This was significant not only as a defense of the newly independent nations of Latin America but also as a foundational element in U.S. foreign policy that emphasized a sphere of influence in the Western Hemisphere. By establishing this doctrine, the U.S. asserted itself as a protector of the Americas, effectively pushing back against European imperial ambitions in the region.

The other options represent different historical policies and initiatives that do not pertain to the same context: The Truman Doctrine was focused on containing communism, the Marshall Plan was about rebuilding Europe after World War II, and the New Deal referred to domestic programs aimed at recovering from the Great Depression. Thus, the Monroe Doctrine is uniquely positioned as the correct answer to the question regarding opposition to European colonialism in the Americas.