What was the Roosevelt Corollary? What did it do?

A corollary (1904) to the Monroe Doctrine, asserting that the U. S. might intervene in the affairs of an American republic threatened with seizure or intervention by a European country, Monroe Doctrine had sought to prevent European intervention, the Roosevelt Corollary was used to justify US intervention throughout the hemisphere. In 1934, President Franklin D. Roosevelt renounced interventionism and established his Good Neighbor policy for the Western Hemisphere.