Why was it that, while Italy could not and would not do without Rome, Germany was compelled to surrender Vienna and to exclude Austria?
The answer is: because the unification of Germany was only possible through the instrumentality of Prussia, which would not brook the rivalry of Austria, and therefore the latter had to go.
The problem of the making of Germany as it presented itself to the mind of Bismarck was first of all a problem as to which should be _supreme_ in Germany, Prussia or Austria; in other words Bismarck cared more for the aggrandisement of Prussia than for the unity of Germany.[1] To the mind of Cavour the problem of the unification of Italy presented itself in a totally different light.

For him there was no question of the aggrandisement of Piedmont, though he no doubt felt pride in the thought that the House of Savoy was to possess the throne of Italy.

Austria was expelled from Italy in 1860, not that Piedmont might take her place as ruler of the peninsula, but that Piedmont might disappear in the larger whole of an emancipated Italy.

Austria was expelled from Germany in 1866 in order that Prussia might rule undisturbed.

Thus, though the Austro-Prussian War of 1866 was an essential step in the foundation of the modern German State, its motives and results were not in the least comparable to those which inspired and followed the Italian War of Liberation in 1859-60.