Monroe Doctrine: A policy introduced in 1823 by President James Monroe which stated that any European colonization efforts in the Americas would be seen as acts of aggression towards the United States.
Truman Doctrine: A policy introduced by President Harry S. Truman in 1947 which aimed to contain communism and support countries resisting Soviet influence through military aid and economic assistance.
Roosevelt Corollary: An addition to the Monroe Doctrine proposed by President Theodore Roosevelt in 1904, stating that the United States had the right to intervene militarily in Latin American countries if their governments were deemed unstable or threatened American interests.