What policy warns European nations against colonization in the Western Hemisphere?

The Monroe Doctrine is the correct answer because it was a significant policy articulated by President James Monroe in 1823, which warned European nations against further colonization and interference in the Western Hemisphere. This doctrine asserted that the Americas were no longer to be considered as subjects for future colonization by any European powers. The context of this policy was rooted in the desire to protect newly independent nations in Latin America from European imperial ambitions, particularly after the period of decolonization in the Americas. The Monroe Doctrine established the foundation for U.S. foreign policy in the region by stating that any attempt by European nations to extend their control in the Americas would be viewed as a threat to U.S. security and would provoke U.S. intervention.

The other policies mentioned, such as the Truman Doctrine, Roosevelt Corollary, and Eisenhower Doctrine, address different geopolitical contexts and issues. The Truman Doctrine focused on containing communism, the Roosevelt Corollary expanded the Monroe Doctrine to justify intervention in Latin America on the grounds of stabilizing countries, and the Eisenhower Doctrine aimed at the Middle East during the Cold War. Each of these doctrines served distinct purposes and responded to different historical circumstances, but none specifically addressed the warning against European colonization in the Western Hemisphere as the