To understand aright the modern concept of neutrality as it existed on the eve of the World War, it is necessary to inquire into its relationship to the society and law of nations. Neutrality, as is well known, was a status almost unknown to the ancient world in the period previous to the establishment of the pax Romana. Once almost universal dominion had passed into the hands of Rome, the possibility of maintaining an impartial attitude as between the Roman Empire and its enemies virtually ceased to exist, and the tribes and peoples bordering the lands where Roman authority was exercised became either hostes or socii et amici. When the Roman imperator was succeeded as a temporal authority by the pontifex maximus of the Christian church, the Mediaeval Empire, embodying in theory the whole of Latin Christendom, went forth against Moor or Saracen alike, conquering and to conquer in the name of the church militant. The foes of the church were the foes of every Christian potentate, and there could be no lukewarmness, no neutrality, in the perennial conflict against the Infidel.