How was the United States able to initially enforce the Monroe Doctrine?

Question

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America funded militias in Latin America to fight the Europeans.
Britain, who supported the doctrine, used their navy to prevent Europeans from building new colonies in the Americas.
President Monroe approved the rapid expansion of the army and nacy.
Russia, who supported the doctrine, used their navy to prevent Europeans from building new colonies in the Americas.

Answer 1

The correct answer is: America funded militias in Latin America to fight the Europeans.