The Monroe Doctrine basically meant that the US wouldn’t tolerate any interventions of the European powers in America and the US wouldn’t intervene in Europe in return.
The Monroe Doctrine covered the entire Western Hemisphere, not just America.
The Monroe Doctrine, first outlined in a speech to Congress in 1823, had President James Monroe warning European powers to not attempt further colonization, military intervention or other interference in the Western Hemisphere, stating that the United States would view any such interference as a potentially hostile act. Over the centuries, the Monroe Doctrine policy has become a cornerstone of U.S. diplomatic and military policies.
According to Monroe’s message (drafted largely by Adams), the Old World and the New World were fundamentally different, and should be two different spheres of influence. The United States, for its part, would not interfere in the political affairs of Europe, or with existing European colonies in the Western Hemisphere.