Monroe Doctrine

US President James Monroe’s 1823 annual message to Congress contained the Monroe Doctrine, which warned European powers not to interfere in the affairs of the Western Hemisphere. 

The Monroe Doctrine was 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.

In 1962, the Monroe Doctrine was invoked symbolically when the Soviet Union began to build missile-launching sites in Cuba. With the support of the Organization of American States, President John F. Kennedy threw a naval and air quarantine around the island. 

After several tense days, the Soviet Union agreed to withdraw the missiles and dismantle the sites. Subsequently, the United States dismantled several of its obsolete air and missile bases in Turkey.

source:

1. wikipedia

2. http://www.ourdocuments.gov/print_friendly.php?page=&doc=23&title=Monroe+Doctrine+%281823%29