Monroe Doctrine: A U.S policy introduced in 1823 that aimed at keeping European powers from interfering with independent states in Americas; it's an early example isolationism policy.
Neutrality Acts: These were laws passed by Congress during 1930s designed to keep the U.S. out of future wars, reflecting isolationist sentiment following World War I.
Non-interventionism: This is a foreign policy that holds that political rulers should avoid alliances with other nations but still retain diplomacy, and avoid all wars not related to direct self-defense.