How did America's aloofness from European politics contributed to the Second World War?

After the First World War America kept aloof from the European politics and did not join the League of Nations. As a result England all alone could not prevent France from ill-treating Germany. Germany could never forget the humiliation she had to suffer at the hands of France and plunged the whole world once again into darkness. American aloofness helped the military rulers of Germany and Italy to adopt violent and aggressive attitude and they ignored the League of Nations very easily.