The Monroe Doctrine was a policy of the United States which opposed colonialism in the Americas. The doctrine stated that efforts by European states to take control of an independent state in America would be considered an attack on the United States. The doctrine was implemented after almost all colonies of Spain and Portugal had achieved independence from the Portuguese and Spanish empires. One of the reasons why the Monroe Doctrine was so significant was because it allowed the United States to exert its influence over the New World undisturbed.
