In 1823, President James Monroe expressed his opinion to Congress that European powers should not be permitted to interfere in the affairs of the sovereign states of the Americas. However, in a bit of a twist, the United States did not follow the terms of its own policy. In 1904, President Theodore Roosevelt added the Roosevelt Corollary to the Monroe Doctrine, which effectively allowed the United States to intervene in Latin American affairs and made the region part of its sphere of influence. Students seeking to learn about the specific details behind this influential policy should look no further than ""The Monroe Doctrine"", one of the insightful titles from the new ""Milestones in American History"" series.