Well the U.S joined the war because of peral harbor. I have to assume you mean prior to Dec 7, 1941. For after that the US was hardly neutral. Prior to that bombing of Pearl Harbor the United States basic policy was one of neutrality and isolationism stemming from WWI. President Roosevelt did offer and aid through material sources help to Great Britain prior to our delcaration of war on Germany.Supplies were sent and guarded by the US Navy to England throughout the early years of 1940 and 1941. hope it helped