“The United States not only helped to encircle Germany with a strangle-hold but continued to maintain that starvation blockade for more than seven months after the Armistice, on the ground that if the blockade were lifted Germany might refuse to accept the peace treaty. No sane American desired to prolong the process of starving German women and children; this atrocity was continued because it was considered necessary. No idea is more inextricably interwoven into war than the doctrine of military necessity.”