Which U.S. policy aimed to prevent European intervention in Latin America?

The policy that aimed to prevent European intervention in Latin America is the Monroe Doctrine. Introduced by President James Monroe in 1823, this doctrine asserted that the Western Hemisphere was off-limits to new European colonialism. Monroe declared that any attempt by European powers to interfere with the nations in the Americas would be viewed as an act of aggression, requiring U.S. intervention. This was an important assertion of U.S. influence in Western affairs and laid the groundwork for future American foreign policy in the region.

In contrast, the other options do not directly relate to this specific goal. The Marshall Plan focused on European economic recovery after World War II; the New Deal was aimed at addressing the economic crisis of the Great Depression within the United States; and the Roosevelt Corollary was an expansion of the Monroe Doctrine in the early 20th century that justified U.S. intervention in Latin America under certain circumstances, but it did not serve as the original policy to prevent European involvement.