Roosevelt adds a Corollary to the Monroe doctrine stating that the "wrongdoings", referring to European interests could need an intervention. he also claimed that said intervention should be made through a civilized nation, meaning the United States of America.
The "policing of the Western Hemisphere" is a phrase that conveys Roosevelt's attitude when it came to international affairs. Roosevelt believed that the United States was justified in exercising this policing for several reasons. He argued that there had been chronic unrest or wrongdoing in the Western Hemisphere for a very long time, and someone had to put an end to it. Moreover, he stated that the United States would intervene in conflucts between European countries and Latin American countries if the European powers had a legitimate claim. He argued that this attitude would work because it came hand in hand with the Monroe Doctrine. While the Monroe Doctrine was meant to put an end to European intervention, the "corollary" (which stated the US intention to police the hemisphere) was used to justify American intervention.