From 1919-1941 the US advocated its isolationism. However, as such a large and economically influential nation it could not be truly isolationist and did take part in some international affairs during the period. The extent to which the nation was isolationist varied throughout the period. One can clearly state that in 1919 support for isolationism was extremely strong but was near completely extinguished by 1942.
After the First World War and partly as a reaction to it, there existed a strong isolationist sentiment among the American people. Forgetting the domestic social reform of the Progressive era many Americans resented its interventionist stance and wished to go back to the isolationist foreign policy of the Guilded Age. In 1920, President Harding called this going back to normalcy'.
"America's present need is not heroics but healing, not nostrums but normalcy, not revolution but restoration .not submergence in internationality but sustainment in triumphant nationality."
Due to this attitude and the need to satisfy it, the US government presented itself as isolationist during the period and was limited in the extent of its intervention in foreign affairs. Public acts of withdraw from international affairs in the 1920s quieted the call for isolationism at home, such as its refusal to join the League of Nations or the International Court of Justice (in 1922 and 1927), failure to ratify the Treaty of Versailles and other isolationist policy like the restrictions on immigration and raised tariffs on European goods.
Although the United States appeared isolationist in the 1920s it cannot be called truly isolationist as policy remained interventionist over some issues. Although it did not join the League of Nations it worked closely with them especially over humanitarian issues. It also instigated and signed the Kellog-Briande Pact in 1928 along with 63 other nations,...