What stated that the United states would not take sides with any European countries at war with one another?

The principle that the United States would not take sides in European conflicts is encapsulated in the Monroe Doctrine, articulated by President James Monroe in 1823. This doctrine asserted that any European intervention in the Americas would be viewed as a threat to U.S. security, while also indicating that the U.S. would remain neutral in European wars. The emphasis on non-intervention was a key aspect of American foreign policy during that era.