When did the USA try isolationism and have it not work. If you refer to WWI and WWII, the USA was hardly isolationist in either of those conflicts. Between the embargoing of Japan in WWII (which was reasonable, and Japan's attack on pearl harbor very stupid), and US ships following German U-boats and broadcasting locations, they were hardly impartial. In WWI the Lusitania was actually found to be carrying weapons. The US has not done real isolationism.