The Monroe Doctrine is a policy of the United States introduced on December 2, 1823. It stated that further efforts by European nations to colonize land or interfere with states in North or South America would be viewed as acts of aggression requiring U.S. intervention. The Doctrine noted that the United States would neither interfere with existing European colonies nor meddle in the internal concerns of European countries. The Doctrine was issued at a time when nearly all Latin American colonies of Spain and Portugal had achieved independence from the Spanish Empire (except Bolivia, which became independent in 1825, and Cuba and Puerto Rico). The United States, working in agreement with Britain, wanted to guarantee no European power would move in.

President James Monroe first stated the doctrine during his seventh annual State of the Union Address to Congress. It became a defining moment in the foreign policy of the United States and one of its longest-standing tenets, and would be invoked by many U.S. statesmen and several U.S. presidents, including Theodore Roosevelt, John F. Kennedy, Ronald Reagan and others.

James Monroe (April 28, 1758 – July 4, 1831) was the fifth President of the United States (1817–1825). Monroe was the last president who was a Founding Father of the United States, and the last president from the Virginia dynasty and the Republican Generation. His presidency was marked both by an "Era of Good Feelings" – a period of relatively little partisan strife – and later by the Panic of 1819 and a fierce national debate over the admission of the Missouri Territory. Monroe is most noted for his proclamation of the Monroe Doctrine in 1823, which stated that the United States would not tolerate further European intervention in the Americas.

Born in Westmoreland County, Virginia, Monroe fought in the American Revolutionary War. He was injured in the Battle of Trenton with a musket ball to his shoulder. After studying law under Thomas Jefferson from 1780 to 1783, he served as a delegate in the Continental Congress. As an anti-federalist delegate to the Virginia convention that considered ratification of the United States Constitution, Monroe opposed ratification, claiming it gave too much power to the central government. Nonetheless, Monroe took an active part in the new government and in 1790 he was elected to the Senate of the first United States Congress, where he joined the Jeffersonians. He gained experience as an executive as the Governor of Virginia and rose to national prominence when as a diplomat in France he helped negotiate the Louisiana Purchase in 1803. Monroe was of French and Scottish descent.