The Seven Weeks’ War, by creating the North German Confederation, a powerful new state in the heart of central Europe, abruptly altered the system of international relations on the Continent. Every government now had to reexamine its diplomatic and military position. No nation, however, was affected by the victory of the Prussian armies as directly as France. Emperor Napoleon III had encouraged hostilities between Austria and Prussia on the assumption that both combatants would emerge from the struggle exhausted and that the Second Empire of France could then expand eastward against little resistance. The outcome of the war revealed how shortsighted such calculations had been. Instead of profiting from the conflict between Francis Joseph and William I, Paris suddenly confronted a strong and united German state that presented a serious threat to French interests. The French government was bound to regard this turn of events with suspicion and hostility. It sought to mitigate its discomfiture by seeking compensation in the Rhineland, Luxembourg, or Belgium. But Berlin succeeded in frustrating these plans, and the conviction began to grow in France that sooner or later a struggle with Germany would be unavoidable. The prospect of a new armed conflict was not unwelcome to Bismarck. He wanted to see national unification consummated by the entry of the southern states into the North German Confederation. Yet public opinion south of the Main River remained distrustful. Only a common patriotic struggle against foreign aggression might overcome the reluctance of the south to unite politically with the north. Thus in Berlin as well as in Paris there were reasons for seeking a test of strength. The immediate occasion came in the spring of 1870 with the candidacy of Prince Leopold, a relative of William I, for the throne of Spain, a prospect that appeared to threaten French national security. Bismarck cleverly exploited the ensuing controversy to provoke the French into initiating hostilities in such a way as to inflame German patriotic indignation.

When France learned of Leopold’s acceptance of the offer of the Spanish crown, there were wild protests in Paris and an immediate demand that Leopold be ordered to withdraw. On July 12 his father renounced the Spanish candidature on his behalf. This was not enough for the French government; it insisted that William I, as head of the Hohenzollern family, should promise that the candidature would never be renewed. This demand was presented to William at Ems by the French ambassador. Though William refused to give a promise, he dismissed the ambassador in a friendly enough way. But when the Ems telegram, a report of the encounter, reached Bismarck, he shortened it for publication to imply that the French ambassador had insulted William and that the king had refused to see the French ambassador again. The French used the king’s supposed refusal as an excuse to declare war on Prussia on July 19.

Bismarck’s calculation that a struggle waged ostensibly against the aggression of Napoleon III would overcome particularism south of the Main River proved correct. The southern states joined the north in the Franco-Prussian War, and the brotherhood of arms brought a sense of unity that was soon enhanced by the intoxication of victory. The German troops won one battle after another in hard fighting along the frontier, until on September 2 they forced a large French army, headed by the emperor himself, to surrender at Sedan. The result was the establishment of a republican government in France, which continued to wage the struggle in the name of the old revolutionary ideals of 1793. The generalship of Moltke and the might of the German armies, however, were too much for the fierce determination of the new regime. Paris capitulated on January 28, 1871, after a long and bitter siege, and on May 10 the Treaty of Frankfurt brought the war officially to a close. The Third Republic had to cede Alsace-Lorraine to Germany, pay an indemnity of five billion francs, and accept an army of occupation. It was a peace designed to crush a dangerous rival. The work of national unification in Germany, in the meantime, was successfully completed even before hostilities had ended. Bismarck had entered into negotiations with the southern states soon after the outbreak of war, determined to use patriotic fervour as an instrument for achieving political consolidation. The enthusiasm aroused in Germany by the victory over France proved too much for the defenders of particularism. On January 18, while Prussian guns bombarded Paris, William I was proclaimed emperor of a united nation at military headquarters in Versailles. The governments south of the Main River joined the North German Confederation to form a powerful new Reich under the Hohenzollerns. Within a single lifetime, Germany had completed the transition from cosmopolitanism to nationalism, from serfdom to industrialization, from division to union, from weakness to dominance, from the Holy Roman Empire to the German Empire.