Final answer:
The true statement about the Monroe Doctrine is that it signaled to Europe that the Western Hemisphere was closed to further colonization, a key element of U.S. policy established in 1823.
Step-by-step explanation:
The statement that is TRUE about the Monroe Doctrine is A) It gave Europe the message that the Western Hemisphere was no longer open for colonization. This doctrine was an important aspect of U.S. foreign policy, established by President James Monroe in 1823. Secretary of State John Quincy Adams, who played a key role in drafting the statement, was instrumental in reinforcing the idea that the Western Hemisphere was to be free from future European colonization endeavors as well as political meddling, asserting the unique position of the United States in global affairs. It is critical to note that the Doctrine itself did not call for immediate military intervention in Latin American countries or impose an embargo on European competitions for colonies in Africa and Southeast Asia, which is what made options B and D incorrect.