Final answer:
The Monroe Doctrine, declared by the United States in 1823, stated that the Americas were no longer open to new European colonization and warned against interference in the Western Hemisphere.
Step-by-step explanation:
The position of the United States in the Monroe Doctrine was A. It declared that the Americas were closed to further European colonization. The Monroe Doctrine, articulated in 1823, was a significant policy statement by President James Monroe that primarily aimed to prevent European powers from establishing new colonies or intervening in the affairs of the independent nations of the Western Hemisphere. The United States, under Secretary of State John Quincy Adams, wanted to proclaim their own principles rather than joining Britain in a joint statement. This foreign policy stance served as a warning against European colonial ambitions and has been interpreted as an assertion of the United States' sphere of influence in the Americas.