(5) A fifth factor was the custom of the great States of keeping standing armies, a custom which also dates from the fifteenth century. The uniform and stern discipline in these armies favoured the rise of more universal rules and practices of warfare.
(6) A sixth factor was the Renaissance and the Reformation. The Renaissance of science and art in the fifteenth century, together with the resurrection of the knowledge of antiquity, revived the philosophical and aesthetical ideals of Greek life and transferred them to modern life. Through their influence the spirit of the Christian religion took precedence of its letter. The conviction awoke everywhere that the principles of Christianity ought to unite the Christian world more than they had done hitherto, and that these principles ought to be observed in matters international as much as in matters national. The Reformation, on the other hand, put an end to the spiritual mastership of the Pope over the civilised world. Protestant States could not recognise the claim of the Pope to arbitrate as of right in their conflicts either between one another or between themselves and Catholic States.
(7) A seventh factor made its appearance in connection with the schemes for the establishment of eternal peace which arose from the beginning of the fourteenth century. Although these schemes were utopian, they nevertheless must have had great influence by impressing upon the Princes and the nations of Christendom the necessity for some kind of organisation of the numerous independent States into a community. The first of these schemes was that of the French lawyer, Pierre Dubois, who, as early as 1306, in "De Recuperatione Terre Sancte" proposed an alliance between all Christian Powers for the purpose of the maintenance of peace and the establishment of a Permanent Court of Arbitration for the settlement of differences between the members of the alliance.[37] Another project arose in 1461, when Podiebrad, King of Bohemia from 1420-1471, adopted the scheme of his Chancellor, Antoine Marini, and negotiated with foreign courts the foundation of a Federal State to consist of all the existing Christian States with a permanent Congress, seated at Basle, of ambassadors of all the member States as the highest organ of the Federation.[38] A third plan was that of Sully, adopted by Henri IV. of France, which proposed the division of Europe into fifteen States and the linking together of these into a federation with a General Council as its highest organ, consisting of Commissioners deputed by the member States.[39] A fourth project was that of Émeric Crucée, who, in 1623, proposed the establishment of a Union consisting not only of the Christian States but of all States then existing in the whole of the world, with a General Council as its highest organ, seated at Venice, and consisting of ambassadors of all the member States of the Union.[40]