Simplify the following text for a Grade 10 native English-speaking person.
Original: The Roosevelt Corollary to the Monroe Doctrine was a substantial alteration ( called an `` amendment '' ) of the Monroe Doctrine by U.S. President Theodore Roosevelt in 1904 . In its altered state , the Monroe Doctrine would now consider Latin America as an agency for expanding U.S. commercial interests in the region , along with its original stated purpose of keeping European hegemony from the hemisphere .
Simplified: The first and most important presidential doctrine was the Monroe Doctrine by President James Monroe stated that the United States declared the right to have influence over Latin America and the U.S. threatened war to any European country which interfered .