(December 2, 1823), cornerstone of U.S foreign policy enunciated by President James Monroe (Monroe, James) in his annual message to Congress. Declaring that the Old World and New World had different systems and must remain distinct spheres, Monroe made four basic points: (1) The United States would not interfere in the internal affairs of or the wars between European powers; (2) the United States recognized and would not interfere with existing colonies and dependencies in the Western Hemisphere; (3) the Western Hemisphere was closed to future colonization; and (4) any attempt by a European power to oppress or control any nation in the Western Hemisphere would be viewed as a hostile act against the United States. (Click here to view the text of the Monroe Doctrine (James Monroe: The Monroe Doctrine).)

The doctrine was an outgrowth of concern in both England and the United States that the continental powers would attempt to restore Spain's former colonies, in Latin America, many of which had become newly independent nations. The United States was also concerned about Russia's territorial ambitions in the northwest coast of North America. As a consequence, George Canning (Canning, George), the British foreign minister, suggested a joint U.S.-British declaration forbidding future colonization in Latin America (Latin America, history of). Monroe was initially favourable to the idea, and former presidents Thomas Jefferson (Jefferson, Thomas) and James Madison (Madison, James) concurred. But Secretary of State John Quincy Adams (Adams, John Quincy) argued that the United States should issue a statement of American policy exclusively, and his view ultimately prevailed.

The Monroe Doctrine, in asserting unilateral U.S. protection over the entire Western Hemisphere, was a foreign policy that could not have been sustained militarily in 1823. Monroe and Adams were well aware of the need for the British fleet to deter potential aggressors in Latin America. Because the United States was not a major power at the time and because the continental powers apparently had no serious intentions of recolonizing Latin America, Monroe's policy statement (it was not known as the “Monroe Doctrine” for nearly 30 years) was largely ignored outside the United States.

The United States did not invoke it nor oppose British occupation of the Falkland Islands in 1833 or subsequent British encroachments in Latin America. In 1845 and again in 1848, however, President James K. Polk (Polk, James K.) reiterated Monroe's principles in warning Britain and Spain not to establish footholds in Oregon, California, or Mexico's Yucatan peninsula. (Click here to view the text of Polk's “Reaffirmation of the Monroe Doctrine.” (James K. Polk: Reaffirmation of the Monroe Doctrine)) At the conclusion of the Civil War, the United States massed troops on the Rio Grande in support of a demand that France withdraw its puppet kingdom from Mexico. In 1867—in part due to U.S. pressure—France withdrew.

After 1870 interpretation of the Monroe Doctrine became increasingly broad. As the United States emerged as a world power, the Monroe Doctrine came to define a recognized sphere of influence. President Theodore Roosevelt (Roosevelt, Theodore) added the Roosevelt Corollary to the Monroe Doctrine in 1904; it stated that, in cases of flagrant and chronic wrongdoing by a Latin American nation, the United States could intervene in the internal affairs of that nation. Roosevelt's assertion of hemispheric police power was designed to preclude violation of the Monroe Doctrine by European countries seeking redress of grievances against unruly or mismanaged Latin American states.

From the presidency of Theodore Roosevelt to that of Franklin Roosevelt, the United States frequently intervened in Latin America, especially in the Caribbean. Since the 1930s, the United States has attempted to formulate its Latin American foreign policy in consultation with the individual nations of the hemisphere and with the Organization of American States. Yet the United States continues to exercise a proprietary role at times of apparent threat to its national security, and the Western Hemisphere remains a predominantly U.S. sphere of influence.

Charles Evan Hughes (Hughes, Charles Evans)'s article on the Monroe Doctrine appeared in the 14th edition of the Encyclopædia Britannica (see the Britannica Classic: ).