Which policy warned European powers to stay out of the Western Hemisphere?

• A. Open Door Policy
• B. Roosevelt Corollary
• C. Monroe Doctrine
• D. Isolationism

Answer: (C)

The Monroe Doctrine sets the standard here. It declared that the Western Hemisphere should be free from future European colonization and interference, and it signaled that the United States would oppose European attempts to meddle in American affairs. That direct warning to European powers to stay out of the Western Hemisphere is exactly what the question is asking about. The Open Door Policy deals with China and trade rights, the Roosevelt Corollary later used the Monroe Doctrine to justify intervention, and Isolationism describes a broader stance rather than a specific warning to Europe about the Western Hemisphere.