The dangers of this growing disunion were sufficiently obvious in the fourteenth and fifteenth centuries. It seemed [Sidenote: Dangers to Germany.] almost inevitable that Germany would lose all semblance of a state, and that as it fell to pieces foreign powers would seize upon the fragments. In the south-east the Turks were gradually establishing themselves on the ruins of the Byzantine Empire, and threatened to advance up the valley of the Danube into the heart of southern Germany. Further north a powerful Slav kingdom was erected in Poland under the House of Jagellon, whose mission seemed to be to annihilate the progress which German influences had effected by means of the Teutonic knights. The Slav kingdom of Bohemia, which under the House of Luxemburg had become almost the capital of Germany, revolted against the rule and the religion of its kings, and the Hussite victories revealed more clearly than any other single event the rottenness and impotence of the existing system in Germany. In the north, the Union of Kalmar brought the three Scandinavian states under a single ruler, and threatened to deprive the German Hansa of the ascendency in northern waters which Lübeck and its associates had gained by their victory over Waldemar III. of Denmark. In the south, the Swiss Confederation was tending to free itself from even nominal dependence on the Empire, and there were other leagues in Swabia and on the Rhine which were not unlikely to follow its example. In the west, German weakness had already allowed France to swallow a great part of the old kingdom of Arles, and though France was for a time crippled by the war with England and by internal dissensions, a new and more pressing danger was created by the rapid growth of the Valois dukes of Burgundy, who absorbed one imperial fief after another, and at one time almost succeeded in building up a middle kingdom along the Rhine, which would have excluded Germany from all real influence on the development of western Europe.