It was a policy for isolationism. At that time, many Americans were still recovering from the losses they incurred in World War I. Apart from that they had to deal with an economic depression that left many unemployed and in poverty. Later as Germany began a massive military campaign in Europe, the U.S. began to worry about the aggression of the Germans and later gave aid to the British and French governments in the form of money and arms. When the Japanese attacked Pearl Harbor, the U.S. formally entered the Second World War.