France declared war on Prussia, turning a diplomatic crisis into a major European conflict. The Prussian-led North German Confederation used rapid rail-based mobilization and a centralized general staff to assemble forces quickly, and South German states sided with Prussia as France was seen as the aggressor. This set the conditions for fast German advances into eastern France.
German forces surprised and defeated a small French garrison at Wissembourg in Alsace. The battle was the first major clash of the war and showed how quickly German armies could concentrate at the border. It helped push French forces back toward larger defensive positions.
On the same day, France lost major battles at Wörth (Frœschwiller-Wœrth) and Spicheren (Forbach). These setbacks forced French armies to pull back toward Metz and other fortified areas. The early defeats made it harder for France to coordinate a stable defense.
At Mars-la-Tour, German forces intercepted the French Army of the Rhine as it tried to move west away from Metz. The fighting helped prevent the French from breaking out toward Verdun. This contributed to the later trapping of a large French army near Metz.
At Gravelotte–St. Privat, German armies fought to stop the French from reopening the road west from Metz. After the battle, the French Army of the Rhine retreated into Metz instead of counterattacking. This decision helped lead directly to the Siege of Metz.
German forces began surrounding Metz, cutting off Marshal François Bazaine’s Army of the Rhine. With a major French army trapped behind fortress defenses, Germany could redirect other forces against remaining French field armies and eventually toward Paris. Metz became a strategic turning point because it removed experienced French troops from active operations.
Germany decisively defeated the French army at Sedan, leading to the surrender of Emperor Napoleon III. The loss destroyed the main remaining imperial field force and shocked French politics. It opened the way for a change of regime and continued fighting under new leadership.
In Paris, political leaders proclaimed a republic and formed the Government of National Defense. Even after the imperial collapse, the new government chose to continue resistance rather than accept immediate peace terms. This decision made the defense of Paris and the creation of new field armies central to the next phase of the war.
German forces completed the investment (encirclement) of Paris and began a prolonged siege designed to force surrender through isolation and shortages. The city relied heavily on National Guard units and fortifications, while the government tried to organize relief armies outside the capital. The siege turned the war into a contest of endurance and political will.
Léon Gambetta left besieged Paris by balloon to help direct the war effort from outside the city. His escape symbolized the government’s attempt to keep fighting by raising and supplying new armies in the provinces. It also highlighted how the siege cut normal communication and travel.
After more than two months of siege, Metz capitulated and the French Army of the Rhine was taken prisoner. The surrender removed one of France’s largest remaining military forces. It enabled Germany to shift troops to other fronts, increasing pressure on Paris and provincial French armies.
German forces defeated the French Army of the Loire near Le Mans. The loss weakened France’s ability to organize effective relief for Paris from the west. As relief attempts failed, the siege’s economic and food pressure on Paris intensified.
German leaders proclaimed King William I of Prussia as German emperor in the Hall of Mirrors at Versailles. The timing and location connected German unification directly to victory over France. Politically, it signaled that the war was reshaping Europe’s balance of power, not just changing borders.
With food and options running out, Paris agreed to an armistice and surrendered after more than four months under siege. The fall of the capital was a decisive military and psychological blow, even though fighting had continued elsewhere. The armistice also set the stage for political conflict inside France over responsibility and the next form of government.
Tensions in Paris rose after the armistice, especially around the National Guard and fears of a conservative political settlement. An uprising on March 18 led to the establishment of the Paris Commune, a revolutionary city government. The episode showed how the siege and defeat intensified social divisions and made postwar stabilization harder.
Germany and the French Third Republic signed the Treaty of Frankfurt, formally ending the war. The settlement confirmed Germany’s new imperial status and imposed major costs on France, including territorial concessions and a large indemnity. It closed the unification-era conflict with a clear outcome: a unified German Empire and a defeated, reorganizing France.
Franco‑Prussian War, German mobilization and the Siege of Paris (1870–1871)