The first part of the monroe doctrine tells european powers are

That they should not claim colonies in the Americas

Explanation:

On 2 December 1823, President James Monroe of the United States of America while addressing the Congress articulated that European powers should acknowledge Western hemisphere a the United States sphere of interest. This is called as Monroe Doctrine and had great influence in the United States foreign policies in the years to come. The interference in the puppet government of Mexico, crises in Cuba were seen as a result of this doctrine.

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