The unification of Germany into a politically and administratively integrated nation state officially occurred on 18 January 1871, in the Hall of Mirrors at the Palace of Versailles in France. Princes of the German states, excluding Austria-Hungary, gathered there to proclaim William I of Prussia as German Emperor after the French capitulation in the Franco-Prussian War. Unofficially, the de facto transition of most of the German-speaking populations into a federated organization of states had been developing for some time through alliances formal and informal between princely rulers, but in fits and starts. The self-interests of the various parties hampered the process over nearly a century of autocratic experimentation, beginning in the era of the Napoleonic Wars, which prompted the dissolution of the Holy Roman Empire in 1806, and the subsequent rise of German nationalism.
Unification exposed tensions due to religious, linguistic, social, and cultural differences among the inhabitants of the new nation, suggesting that 1871 only represented one moment in a continuum of the larger unification processes. The Holy Roman Emperor had been often called "Emperor of all the Germanies"; contemporary news accounts frequently referred to "The Germanies". In the empire, higher nobility were referred to as "Princes of Germany" or "Princes of the Germanies"—for the lands once called East Francia had been organized and governed as pocket kingdoms since before the rise of Charlemagne (800 AD). In the mountainous terrain of much of the territory, isolated peoples developed cultural, educational, linguistic, and religious differences over such a lengthy time period. By the nineteenth century, transportation and communications improvements brought these regions closer together.
The Holy Roman Empire, which had included more than 500 independent states, was effectively dissolved when Emperor Francis II abdicated (6 August 1806) during the War of the Third Coalition. Despite the legal, administrative, and political disruption associated with the end of the Empire, the people of the German-speaking areas of the old Empire had a common linguistic, cultural, and legal tradition further enhanced by their shared experience in the French Revolutionary Wars and Napoleonic Wars. European liberalism offered an intellectual basis for unification by challenging dynastic and absolutist models of social and political organization; its German manifestation emphasized the importance of tradition, education, and linguistic unity of peoples in a geographic region. Economically, the creation of the Prussian Zollverein (customs union) in 1818, and its subsequent expansion to include other states of the German Confederation, reduced competition between and within states. Emerging modes of transportation facilitated business and recreational travel, leading to contact and sometimes conflict among German speakers from throughout Central Europe.
The model of diplomatic spheres of influence resulting from the Congress of Vienna in 1814–15 after the Napoleonic Wars endorsed Austrian dominance in Central Europe. The negotiators at Vienna took no account of Prussia's growing strength within and among the German states and so failed to foresee that Prussia would rise to challenge Austria for leadership of the German peoples. This German dualism presented two solutions to the problem of unification: Kleindeutsche Lösung, the small Germany solution (Germany without Austria), or Großdeutsche Lösung, the greater Germany solution (Germany with Austria).
Historians debate whether Otto von Bismarck—Minister President of Prussia—had a master plan to expand the North German Confederation of 1866 to include the remaining independent German states into a single entity or simply to expand the power of the Kingdom of Prussia. They conclude that factors in addition to the strength of Bismarck's Realpolitik led a collection of early modern polities to reorganize political, economic, military, and diplomatic relationships in the 19th century. Reaction to Danish and French nationalism provided foci for expressions of German unity. Military successes—especially those of Prussia—in three regional wars generated enthusiasm and pride that politicians could harness to promote unification. This experience echoed the memory of mutual accomplishment in the Napoleonic Wars, particularly in the War of Liberation of 1813–14. By establishing a Germany without Austria, the political and administrative unification in 1871 at least temporarily solved the problem of dualism.
, a personification of the German nation, appears in Philipp Veit
's fresco (1834–36). She is holding a shield with the coat of arms of the German Confederation. The shields on which she stands are the arms of the seven traditional Electors
of the Holy Roman Empire.
- 1797: The French First Republic annexed the Left Bank of the Rhine as a result of the War of the First Coalition.
- 1802: Previous annexations by France confirmed following its victory in the War of the Second Coalition.
- 1804: Francis I of Austria declared the new Austrian Empire as a reaction to Napoleon Bonaparte's proclamation of the First French Empire in 1804.
- 1806: As a result of the War of the Third Coalition, Napoleon I annexed some territories East of the Rhine, replaced the Holy Roman Empire by the Confederation of the Rhine as a French client-state.
- 1807: Prussia lost one half of its territory following the War of the Fourth Coalition.
- 1815: After the defeat of Napoleon, the Congress of Vienna reinstated the Germanic states into the German Confederation under the leadership of the Austrian Empire.
- 1819: The Carlsbad Decrees suppressed any form of pan-Germanic activities to avoid the creation of a 'German state'; the Kingdom of Prussia, however, initiated a customs union with other Confederation states.
- 1834: The Prussian-led custom union evolved into the Zollverein that included almost all Confederation states except the Austrian Empire.
- 1848: Revolts across the German Confederation, such as in Berlin, Dresden and Frankfurt, forced King Frederick William IV of Prussia to grant a constitution to the Confederation. In the meantime, the Frankfurt Parliament was set up in 1848 and attempted to proclaim a united Germany, but this was refused by William IV. The question of a united Germany under the Kleindeutsch solution (to exclude Austria) or the so-called Großdeutsch (to include Austria) began to surface.
- 1850: The Erfurt Union was a short-lived attempt at a union of German states under a federation, proposed by the Kingdom of Prussia. The Erfurt Union Parliament (Erfurter Union Parliament), lasting from March 20 to April 29, 1850, was opened at the former Augustinian monastery at Erfurt. The union never came into effect, and was completely undermined by the Punctuation of Olmütz, a treaty between Prussia and Austria, signed 29 November 1850, by which Prussia abandoned the Erfurt Union and accepted the revival of the German Confederation under Austrian leadership.
- 1861–62: King Wilhelm I became King of Prussia and he appointed Otto von Bismarck on 23 September 1862, Minister President and Foreign Minister, who favoured a 'blood-and-iron' policy to create a united Germany under the leadership of Prussia.
- 1864: The Danish-Prussian War started as Prussia protested against Danish incorporation of Schleswig into the Kingdom of Denmark. The Austrian Empire was deliberately drawn into this war by Otto von Bismarck, Chancellor of Prussia. The Austro-Prussian victory led to Schleswig, the northern part, being governed by Prussia and Holstein, the southern part, being governed by Austria, as per the Treaty of Vienna (1864).
- 1866: Bismarck accused the Austrian Empire of stirring up troubles in Prussian-held Schleswig. Prussian troops drove into Austrian-held Holstein and took control of the entire state of Schleswig-Holstein. Austria declared war on Prussia and, after fighting the Austro-Prussian War (Seven Weeks' War), was swiftly defeated. The Treaty of Prague (1866) formally dissolved the German Confederation and Prussia created the North German Confederation to include all Germanic states except the pro-French, southern kingdoms of Bavaria, Baden and Württemberg.
- 1870: When the French emperor, Napoleon III, demanded territories of the Rhineland in return for his neutrality amid the Austro-Prussian War, Bismarck used the Spanish Succession Question (1868) and Ems Telegram (1870) as an opportunity to incorporate the southern kingdoms. Napoleon III declared war against Prussia.
- 1871: The Franco-Prussian War ended with Prussian troops capturing Paris, the capital of the Second French Empire. Bavaria, Baden, and Württemberg were incorporated into the North German Confederation in the Treaty of Frankfurt (1871). Bismarck then proclaimed King Wilhelm I, now Kaiser Wilhelm I, as leader of the new, united Germany (German Reich), excluding Austria. With the German troops remaining in Paris, Napoleon III dissolved the French Empire and a new republic, the Third French Republic, was created under Adolphe Thiers.