The Monroe Doctrine is a foreign policy platform established by President James Monroe of the United States. According to his State of the Union address on 2 December 1823, Monroe asserted that no country outside the Western Hemisphere could use its sphere of influence to manipulate the affairs of nations within the region. It essentially stated that the period of colonialism was over and no new powers, specifically those of Europe, were allowed to dominate the political or economic futures of nations in North or South America. Any attempt at such would be considered a threat to the peace and safety of the United States itself. The Monroe Doctrine became a central policy that impacted all future activities of the global community in regards to the New World.
At the time, the United States was not considered a major world power and many contemporaries viewed the policy with only passing interest. After the American Revolution and the Louisiana Purchase, Great Britain and France lost much of its territorial considerations in North America. This was accented by the fact that many of the Spanish colonies in South America were gaining independence through revolutionaries such as Simon Bolivar. This trend opened up much of the Americas to trade deals with new nations, prompting a fear that new colonization attempts would destroy the economic developments of the era. At the same time, the Russian Empire was attempting to assert its dominance in the Northwest with its Alaska territory, prompting a need for the U.S. to make a statement like the Monroe Doctrine.
The overall effect of the Monroe Doctrine on U.S. politics eventually became highly important to the country as it grew to a superpower. With the purchase of Alaska, the U.S. removed Russia's hold on its part of the Western Hemisphere. This was followed at the turn of the century with the U.S. successfully ousting the remnants of European influence during the Spanish-American War. This left the Americas with limited foreign intervention and nearly no political or military clout from any of the Old World powers, with the exception of a few Caribbean islands.
To highlight the policies of the Monroe Doctrine in the early 20th century, President Theodore Roosevelt established the Roosevelt Corollary in 1904. This extended the rights of the U.S. to intervene in Latin America and the Caribbean both militarily and economically. This was slightly adjusted by the Clark Memorandum, a policy adopted by President Calvin Coolidge that reaffirmed the United States' right to deal with Latin America. This new interpretation focused on the fact that American actions were undertaken since the U.S. was an independent state and considered itself a good neighbor to its fellow nations.
The Monroe Doctrine was again invoked during the Cold War, most notably in response to the Communist takeover of Cuba by the Fidel Castro regime. President John F. Kennedy used the principles of the policy to establish an embargo on the island to prevent Soviet weapons from being deployed. The concept was criticized heavily during the Iran-Contra Scandal of the 1980s when it was revealed that the U.S. attempted to overthrow the Sandinista regime in Nicaragua by training and arming guerrilla fighters.