The Monroe Doctrine was enacted in 1823 and described the approach that the US would subsequently adopt in foreign policy issues, positioning themselves against European colonialism in America. The doctrine stated that any attempts conducted by a European country, to gain control over any independent state in America, would be regarded as "the manifestation of an unfriendly disposition toward the US". In such situation, the US would have to react in consequence.
Although the US claimed it intervened in other American countries to help them keep their independence and resist attacks from colonialist nations, the US was acting itself as a colonial power, exercising its influence over previously free nations that became totally dependent.