The Monroe Doctrine is a United States policy introduced on December 2, 1823, which said that further efforts by European governments to colonize land or interfere with states in the Americas would be viewed by the United States of America as acts of aggression requiring US intervention.
President James Monroe first stated the doctrine during his seventh annual State of the Union Address to Congress.
It became a defining moment in the foreign policy of the United States and one of its longest-standing tenets, invoked by U.S. presidents Theodore Roosevelt, Calvin Coolidge, Herbert Hoover, John F. Kennedy, and others.
The Roosevelt Corollary to the Monroe Doctrine (added during the presidency of Theodore Roosevelt) was invoked to intervene militarily in Latin America to stop the spread of European influence.
It would have been impossible for Monroe to envision that its intent and impact would persist with minor variations for almost two centuries. Its primary objective was to free the newly independent colonies of Latin America from European intervention and control. The doctrine advocated that the New World and the Old World were to remain distinctly separate spheres of influence, for they were comprised of entirely separate and independent nations.
It was born from concerns of both the United States and Great Britain that Spain would attempt to restore its influence over Spain's former colonies.
President Monroe claimed the United States of America, although only a fledgling nation at the time, would not interfere in European wars or internal dealings, and in turn, expected Europe to stay out of the affairs of the New World. The Western Hemisphere was never to be colonized again and any attempt by a European power to oppress or control any nation in the Western Hemisphere would be perceived as a direct threat to the U.S.. This quid pro quo was presumptuous on its face, yet has stood the test of time.