Although in some cases wars may be coolly planned by the people’s leaders for personal or political reasons or for purposes of national conquest, still they all depend for their successful issue upon the homicidal impulse in the masses of people. This is called the war spirit and is always of an epidemic character. It may have any degree of ferocity or mildness. It has a tendency to be periodic, so that if it has slumbered for a considerable period a very slight cause is sufficient to awaken it. A mere boundary line in Venezuela, in which this country had but a remote interest, was sufficient a few years ago to excite this war spirit in a milder form, when a curious craze for a war with Great Britain flowed like a wave across this country. Any war will furnish instructive material to the student of social psychology. In the late Spanish-American war, for instance, we all felt the war spirit which flowed in epidemic form across the country and engulfed it. The first motive of the war, the altruistic desire to free an oppressed people, was of the ideal glittering kind, well fitted to excite the emotions of the masses. A dramatic event further fans this emotional flame, and at once the aggregate personality of the nation is in a condition of automatism, where primitive instincts, such as revenge and lust for the paraphernalia of war, are no longer checked by the more lately acquired moral principles. Congressmen, editors, members of peace societies, ministers of the gospel, forget their long and patient efforts to establish means for settling national differences by arbitration and join lustily in the war cry, and the psychologically curious spectacle is presented of a great nation, priding itself as a leader in the world’s morals, giving to the appeal of a weaker nation for the arbitration of a dispute the answer of shot and shell. Although the motive of blood for blood is a moral motive belonging to a bygone age and in individual ethics has long been outgrown, yet collectively, under the influence of the war craze, we revert to it, and it is shamelessly proclaimed from platform and editorial room and vigorously applauded by the people. We have seen that cruelty and the persecution of the weak by the strong were among the reversionary symptoms of the social epidemic in many instances. We may notice curiously enough a trace of these qualities here, where the fact that our enemy was a greatly inferior power does not detract in our eyes from the brilliancy of our victories, though in the ethics of the individual such a circumstance would put us to shame. In all this we proceed strictly in accordance with international law, but international law itself is only international custom and is the mere expression of the wonted behavior of the aggregate personality, particularly in times of war. As such it does not represent the highest ethical development of man, but that lower stage of development to which he reverts in times of social excitement.