In foreign affairs Monroe proclaimed the fundamental policy that bears his name, responding to the threat that the more conservative governments in Europe might try to aid Spain in winning back her former Latin American colonies. Monroe did not begin formally to recognize the young sister republics until 1822, after ascertaining that Congress would vote appropriations for diplomatic missions. He and Secretary of State John Quincy Adams wished to avoid trouble with Spain until it had ceded the Floridas, as was done in 1821. Great Britain, with its powerful navy, also opposed reconquest of Latin America and suggested that the United States join in proclaiming "hands off." Ex-Presidents Jefferson and Madison counseled Monroe to accept the offer, but Secretary Adams advised, "It would be more candid .. to avow our principles explicitly to Russia and France, than to come in as a cock-boat in the wake of the British man-of-war."

Monroe accepted Adams's advice. Not only must Latin America be left alone, he warned, but also Russia must not encroach southward on the Pacific coast. ". . . the American continents," he stated, "by the free and independent condition which they have assumed and maintain, are henceforth not to be considered as subjects for future colonization by any European Power." Some 20 years after Monroe died in 1831, this became known as the Monroe Doctrine. .