A principle of non-intervention in the domestic affairs of another nation is common in many countries. It's also one of the fundamental principles of the United Nations, which says it has "no authority to intervene in matters which are within the domestic jurisdiction of any state [...]." However, some domestic issues make people question how strongly we should support non-interventionism.
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In the United States, non-interventionism has a long history that dates back to the founding fathers. George Washington indicated support for this principle in his Farewell Address, when he encouraged commercial relationships with other countries while keeping "as little political connection as possible." The Monroe Doctrine also supported non-intervention. Later, the Roosevelt Corollary to the Monroe Doctrine altered America's stance substantially, with President Theodore Roosevelt saying the U.S. might "exercise international police power in 'flagrant cases of such wrongdoing or impotence.'" This corollary was used as justification for interventions in Cuba, Nicaragua, Haiti, and the Dominican Republic. It was renounced in 1934 by President Franklin D. Roosevelt.
When conflicts are confined within the borders of a single state, there is often heated debate regarding whether or not other countries have the right or obligation to intervene. Non-interventionism is a common rationale for why outside powers have had limited or no involvement in conflicts where many expected there to be an international response, such as the genocide in Rwanda and the civil war in Syria. Currently, non-interventionism is being offered as a rationale for why U.S. soldiers did not intervene in allegations of child abuse brought against Afghan soldiers.
Read more about non-interventionism:
United Nations: Purposes and Principles of the United Nations
U.S. Department of State: Roosevelt Corollary to the Monroe Doctrine, 1904
U.S. Department of State: Monroe Doctrine, 1823