In theory the Emperor of the Germans remained for hundreds of years to come the master of the world, but in practice he was not even master at home, as the German Princes step by step succeeded in establishing their independence. And although theoretically the world was well looked after by the Emperor as its temporal and the Pope as its spiritual head, there were constantly treachery, quarrelling, and fighting going on. War practice was the most cruel possible. It is true that the Pope and the Bishops succeeded sometimes in mitigating such practice, but as a rule there was no influence of the Christian teaching visible.
[Sidenote: The Fifteenth and Sixteenth Centuries.]
§ 42. The necessity for a Law of Nations did not arise until a multitude of States absolutely independent of one another had successfully established themselves. The process of development, starting from the Treaty of Verdun of 843, reached that climax with the reign of Frederic III., Emperor of the Germans from 1440 to 1493. He was the last of the emperors crowned in Rome by the hands of the Popes. At that time Europe was, in fact, divided up into a great number of independent States, and thenceforth a law was needed to deal with the international relations of these Sovereign States. Seven factors of importance prepared the ground for the growth of principles of a future International Law.
(1) There were, first, the Civilians and the Canonists. Roman Law was in the beginning of the twelfth century brought back to the West through Irnerius, who taught this law at Bologna. He and the other _glossatores_ and _post-glossatores_ considered Roman Law the _ratio scripta_, the law _par excellence_. These Civilians maintained that Roman Law was the law of the civilised world _ipso facto_ through the emperors of the Germans being the successors of the emperors of Rome. Their commentaries to the _Corpus Juris Civilis_ touch upon many questions of the future International Law which they discuss from the basis of Roman Law.
The Canonists, on the other hand, whose influence was unshaken till the time of the Reformation, treated from a moral and ecclesiastical point of view many questions of the future International Law concerning war.[35]