The correct answer is: "the Monroe Doctrine".
The Monroe Doctrine was enacted in 1823 in order to establish the intentions of the US in foreign policy issues. It firmly opposed new forms of European colonialism in America, and stated that any intention from an European state of exercising control over an independent country in North or South America would be regarded as "an unfriendly disposition towards the US", that will have to adopt measures in consequence.
It did not interfere with existing colonies at the time,but the Monroe Doctrine did set a threat in case former colonizers were intending to conquer their old territorial possessions again.
