Before the ambition of Russia gave rise to the Eastern Question the House of Austria was the Christian power chiefly interested in beating back the Turks. The Emperors no doubt felt somewhat the obligation which lay upon them, as the traditional lords of Christendom, to take the lead in the work of emancipating Christian lands and imperial vassals from the yoke of the infidel. But much more did they feel the political necessity which forced them, as kings of Hungary and Croatia and overlords of Transylvania, to make themselves undisputed masters of the valleys of the Danube the Drave and the Save. With the Turks securely planted at Buda, and within striking distance of Agram, Vienna itself was unsafe, and the communications between Austria and Italy liable at any moment to be cut. The more the Emperor was being deprived of leadership in Germany, the more he was being ousted from influence on the Rhine, the more essential it became to him to retain his hold upon the Danube. So during the whole of the seventeenth century the history of south-eastern Europe is the history of a duel between the House of Austria and the Sultans for political and military supremacy on the Danube and the Save. Other combatants such as the French, the Venetians, the Poles and the Russians, appear from time to time and take part in the struggle from motives of ambition or patriotism or interest and most powerfully affect its fortunes, but the essential character of the contest remains unchanged. Austria and the Turks fight for pre-eminence on the Danube, just as Germany and France fight for pre-eminence on the Rhine. [Sidenote: =Misgovernment at Constantinople, 1603–1656.=]