The Monroe Doctrine put forth the policy of separate spheres of influence for the United States and Europe. It stated the intent of the United States to not involve itself in Europe's internal affairs or existing colonies in the Americas and warned Europe that the independent lands of the Western Hemisphere would solely be the domain of the United States.
This doctrine, set forth in President James Monroe's seventh annual message to Congress on Dec. 2, 1823, became a major tenet of U.S. foreign policy. Monroe promised that, "Our policy, in regard to Europe, which was adopted at an early stage of the wars which have so long agitated that quarter of the globe, nevertheless remains the same, which is, not to interfere in the internal concerns of any of its powers..." In exchange for the United States' non-interference, Monroe expected, “The American continents … are henceforth not to be considered as subjects for future colonization by any European powers.”
The United States first invoked the Monroe Doctrine in 1865 in response to the puppet monarch placed on the Mexican throne by the French government. The U.S. government exerted diplomatic and military pressure in support of the Mexican President Benito Juárez, who then led a successful revolt against the French emperor.