The Monroe Doctrine was declared in a few paragraphs of President James Monroe's seventh annual message to Congress on December 2, 1823. Monroe warned European countries not to interfere in the Western Hemisphere, stating "that the American continents...are henceforth not to be considered as subjects for future colonization by any European powers." The Monroe Doctrine became a cornerstone of future U.S. foreign policy. As the United States gained military and economic strength, American leaders began to interpret the Monroe Doctrine as justification for U.S. involvement in Latin America.