Final answer:
The Roosevelt Corollary, an extension of the Monroe Doctrine, was used to justify the United States' involvement in Latin America and helped to bring about the building of the Panama Canal.
Step-by-step explanation:
The policy seen as an extension of the Monroe Doctrine used to facilitate the construction of the Panama Canal was the Roosevelt Corollary. The Monroe Doctrine was a policy established by President James Monroe in 1823 stating that European nations should not interfere in the affairs of the nations in the Western Hemisphere. The Roosevelt Corollary, announced by President Theodore Roosevelt in 1904, extended this policy, essentially stating that the United States had the right to intervene in Latin American nations to preserve stability and order. This was used to justify the United States' involvement in Panama and the subsequent building of the Panama Canal.
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