Roosevelt sent supplies, military equipment, and surplus to help aid the Allies (usually they wouldn't do this until they were part of the war). In doing this, it shows that the US doesn't wait until they get hit, instead they reach out (even though it was only economically, in the case of military, they still waited). Roosevelt also wasn't really the reason the US ended isolationism. It was more of Emperor Hirohito. He allowed his military generals to attack Hawaii for resources and to continue on their expansions of taking over all of the Pacific. Roosevelt only "convinced" (well, all of them were hopping mad already) Congress to declare war on Japan and Germany.
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