He had been wily enough to secure by vague non-committal half-promises the neutrality of France during the weeks while Prussia was crushing the armed strength of Austria in Bohemia. But the issue of Königgrätz startled Napoleon and set France in ferment. Bismarck dared to refuse point-blank the demand which the French Emperor made for the fortress of Mayence, made though that demand was under threat of war. The Prussian commanders would have liked nothing better than a war with France, and Roon indeed had warned for mobilisation 350,000 soldiers to swell the ranks of the forces already in the field; but Bismarck was wise and could wait. He allowed Napoleon to exercise some influence in the negotiations in the character of a mediator; and to French intervention was owing the stipulation that the South German States should be at liberty to form themselves into a South German Confederation of which Napoleon hoped to be the patron. But Bismarck was a better diplomatist than Napoleon. While he formed and knit together the North German Confederation in which Prussia was dominant, he quietly negotiated an alliance offensive and defensive with each of the Southern States separately. No Southern bund was ever formed, and when the Franco-German War broke out in 1870 Napoleon saw the shipwreck of his abortive devices in the spectacle of the troops of Bavaria and Würtemberg marching on the Rhine in line with the battalions of Prussia. The unity of Germany was not yet; that consummation and the Kaisership--the two greatest triumphs of Bismarck's life--required another and a greater war to bring about their accomplishment. During the interval between 1866 and 1870, while the armed strength of Northern Germany was being quietly but sedulously perfected, Bismarck with dexterous caution was smoothing the rough path toward the ultimate unification. He would not have his hand forced by the enthusiasts for "the consummation of the national destiny." "No horseman can afford to be always at a gallop" was the figure with which he met the clamourers of the Customs Parliament. He invoked the terms of the treaty of Prague against the spokesmen of the Pan-German party inveighing vehemently against the policy of delay. He was staunch in his conviction that the South for its own safety's sake would come into the union the moment that the North should engage in war. He was a few weeks out in his reckoning; the Southern States waited until Sedan had been fought, when the prospect of the spoils of victory was assured; and this measured delay on their part was the best justification of Bismarck's sagacious deliberateness. The negotiations were tedious, but at length, on the evening of 23rd November 1870 the Convention with Bavaria was signed, and the unity of Germany was an accomplished fact. Busch vividly depicts the great moment:--