Final answer:
The Monroe Doctrine was addressed to European powers, warning them against further colonization or interference in the Western Hemisphere. It established a U.S. sphere of influence and marked the U.S.’s role in regional stability, which was later reinforced by the Roosevelt Corollary.
Step-by-step explanation:
The Monroe Doctrine was primarily addressed to European nations, particularly those of the Holy Alliance, to discourage them from attempting to colonize or interfere with the newly independent nations of the Western Hemisphere. In 1823, President James Monroe, along with his Secretary of State John Quincy Adams, proclaimed this doctrine within an annual message to Congress. The message indicated that any further colonization by European powers in the Americas would be seen as an act of aggression requiring U.S. intervention. This doctrine established the United States' sphere of influence in the Western Hemisphere and warned European nations to constrain their political activities in the region. Despite the boldness of the doctrine, some were skeptical of how effectively the United States could enforce such a policy against European powers.
Later, the Roosevelt Corollary to the Monroe Doctrine would reinforce the United States' commitment to this policy, with President Theodore Roosevelt asserting that the U.S. might act as an "international police power" to ensure the stability of nations within the Western Hemisphere. This corollary was seen by many in Latin America as justification for American imperialism, as it allowed U.S. intervention in the domestic affairs of neighboring countries.