Whatever Austria's ulterior views may have been, Bismarck certainly from the first had but one aim before him. He saw clearly what the possession of the duchies would mean to Germany, their vast importance for the future of German sea-power; already he had a vision of the great war-harbour of Kiel and the canal connecting the Baltic and the North seas; and he was determined that these should be, if not wholly Prussian, at least wholly under Prussian control. Annexation was the goal which from the beginning he kept steadily before his eyes (_Reminiscences_, ii. 10). As for treaties to the contrary, he was to avow in his _Reminiscences_ that these have little force when no longer reinforced by the interests of the contracting parties. His main fear was that the Danes might refuse to fight and appeal instead to a European congress; and, to prevent this, he led the Copenhagen government to believe that Great Britain had threatened to intervene in the event of Prussia going to war, "though, as a matter of fact, England did nothing of the kind." This sufficed to provoke the defiance of the Danes, and on the 1st of February 1864 the Austrian and Prussian troops crossed the Eider. The issue of a war between powers so ill-matched was a foregone conclusion; the famous rampart of the Dannewerk (q.v.), on which the Danish defence chiefly relied, was turned, and after a short campaign, in which the Danes fought with distinguished courage, peace was concluded by the treaty of Vienna (August 1, 1864), by which Schleswig, Holstein and Lauenburg were ceded to Austria and Prussia jointly. Austria, Prussia and the Zollverein. The Austro-Prussian alliance had been only an interlude in the great drama in which the two powers were playing rival parts. To the other causes of friction between them had been added, just before the war, a renewed quarrel as to Austria's relation to the Zollverein. In 1862, in the name of the customs union, Prussia had concluded with France a commercial treaty, based mainly on free trade principles. This treaty most of the small states refused to sign, and they were supported in their objections by Austria, which loudly complained that Prussia had given to a foreign power what she had denied to a sister state of the _Bund_. Prussia, however, remained firm, and declared that, were the treaty rejected, she would break up the Zollverein. After the war Bismarck in fact succeeded in obtaining the signature of the smaller states to the treaty; and Austria, her protests having proved unavailing, was fain to sign a commercial treaty with the Zollverein, essentially the same as that of 1853. Treaties concluded with Great Britain and Belgium, about the same time, also tended to enhance Prussian prestige. Convention of Gastein.