As a youthful politician, he joined the anti-Federalists in the Virginia Convention which ratified the Constitution, and in 1790, an advocate of Jeffersonian policies, was elected United States Senator.
His ambition and energy, together with the backing of President Madison, made him the Republican choice for the Presidency in 1816. With little Federalist opposition, he easily won re-election in 1820.
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.
Some 20 years after Monroe died in 1831, this became known as the Monroe Doctrine.