Manifest Destiny: The 19th-century doctrine or belief that the expansion of the US throughout the American continents was both justified and inevitable.
Monroe Doctrine: A principle of US policy, originated by President James Monroe in 1823, that any intervention by external powers in the politics of the Americas is a potentially hostile act against the US.
Roosevelt Corollary: An addition to the Monroe Doctrine articulated by President Theodore Roosevelt in his State of Union address in 1904 after the Venezuela Crisis of 1902–03. It stated that not only were European powers not allowed to colonize new areas but they also could not intervene in Latin America.