After the war, Prussia stayed in control of Schleswig and Austria remained in the southern Holstein, which posed the obvious problem for Austria that it now had a territory which was among Prussian territory. Bismarck now finally had his motive for war and Prussia (together with Italy in the south) attacked Austria (supported by Saxony, Hanover, Bavaria, Wurttemberg, Baden, Hesse-Darmstadt, Hesse-Cassel and Nassau). Prussia was able to achieve a straightforward success, due to its superior military equipment, its road and rail network, its larger force and because Austria had to fight a two-front war. The war was over with the treaty of Prague in August 1866, and Prussia formed all German territories north of the river Main into a North German Confederation from which Austria was excluded. Bismarck also renewed the Zollverein in this year to exclude Austria and bring further unity to the German states. However Austria "only" had to cede its influence in Germany and the territories of Holstein and Venetia. Bismarck did not want to make the settlements too brutal because he was interested in maintaining good relations with Austria, probably in recognition of his further ambitions in southern Germany and a fear of Austrian alliance with France. The first half of Bismarck's campaign towards Prussian unification of Germany was extremely successful; his strategy of alienating Austria and then provoking her into war worked was a masterpiece of political and military ingenuity and a perfect example of his opportunism.
Although the German north was now united, Bismarck instigated another war to complete the German Unification, this time with France. In 1870 the Spanish throne was empty and one possible successor was Prince Leopold a member of the Prussian Hohenzollern family. France vehemently opposed such a successor because it feared encirclement through Prussia, and wanted to place a member of the Bourbon family on the Spanish throne instead.