Two men had made the Franco-Prussian War, and now only one remained to conclude it. The other, released from his post-Sedan captivity in Kassel, made his doleful way to England in March 1871, to begin his exile with the empress and prince imperial at Camden Place, a twenty-room mansion in Chislehurst, Kent. French republicans watched this gathering of Bonapartes nervously, for recent history suggested that they were, in Emile Zola's words, “a strange family that never dies, which goes on, with its pale and moribund children … with their pockets empty one day, then safes full of money the next. They live in palaces, they die on rocks. They mint coins with our blood. And they are still there, at our throats, or at the bottom of some ditch, watching us and ready to jump on our shoulders.” And yet here was one Bonaparte who would not clamber back; Louis-Napoleon would die of anguish and kidney stones in 1873. Lou-Lou the prince imperial – a Woolwich graduate in the meantime – would follow his father to the grave six years later, killed by Zulus at the age of twenty-three while riding in South Africa with the Natal Horse and attempting to burnish his military credentials for the role of Napoleon IV. Undisputed master of France and Central Europe, Bismarck – “the genius of the actual,” the European statesman most able to divine and interpret current trends – began to fumble in a most uncharacteristic and ultimately tragic way.

The immediate objective of General Tann's new “Army Section” – a Bavarian corps, a Prussian infantry division and two Prussian cavalry divisions – was to find and destroy the French XV Corps under General Joseph La Motterouge. Ordered by War Minister Leflô to “do something for the sake of public opinion,” La Motterouge had drawn in his brigades from Vierzon, Bourges, and Nevers and concentrated them at Orléans. Sent south by Moltke to preempt threats like this and “clear the country between Paris and the Loire,” Tann left Etampes with five divisions in early October.

Marching and eating well in the flat, gold-stubbled Beauce, the Germans made good time. Each cross road that ought to have been held by the French was either deserted or lightly defended, allowing the Germans to punch through easily using their cavalry and guns to maximum advantage on plains so flat and featureless that, as one veteran put it, “the earth and sky swam together before your eyes.” With most of France's regular army in captivity, the Germans collided with a strange soldatesca, including francs-tireurs (irregular “sharpshooters”) and new formations of “partisans.” Because the Germans were summarily executing francs-tireurs – depressing morale among would-be guerrillas – the government at Tours had created semi-official partisan companies that carried government pay books and wore uniforms, albeit outlandish ones. The Partisans de Gers, encountered by the Prussians at Etampes, wore long black coats, black trousers, red scarves, and broad-brimmed Calabrian hats.

As Bismarck had anticipated, France's potential allies in Europe were the first to blench at the news of Spicheren and Froeschwiller. Stunned by the speed of the Prussian attacks, first the Austrians, then the Italians, and finally the Danes stood down, quietly refusing to intervene in a war that the Prussians now looked certain to win. French citizens, fooled by censorship and wild rumors, reacted less surely. Indeed on the day of Spicheren and Froeschwiller, two French swindlers were able to perpetrate a sensational hoax. As crowds of Parisians surged around the Bourse awaiting war news that they assumed would be delivered first to the stock exchange “for the benefit of money-changers and speculators,” one of the two swindlers stationed himself in the entrance of the Bourse while the other, disguised as a courier, rode a lathered horse through the crowd, waving a paper and shouting “official dispatch!” The two accomplices met and the well-dressed one, posing as a spokesman for the Bourse, shouted the “war news” at the top of his lungs: “There has been a great battle, a great French victory, 25,000 Prussians have been captured, including the crown prince and forty guns.”

Elihu Washburne, the U.S. ambassador to France, noted that “a spark of fire falling upon a magazine could not have produced a greater explosion.” The crowd went mad; people clasped one another, kissed, danced, and sang.

Bismarck slept in a hayloft after Gravelotte, woke the next morning and rode across the battlefield with American General Phil Sheridan. Sheridan recalled that they swigged from a bottle of brandy while riding through the “awful carnage.” The “sight was sickening to an extreme,” and the chancellor veered squeamishly into the gaps between the corpses on the way up to Moscou and Leipzig. Lower-ranking Prussians were not so fortunate; they spent the day after Gravelotte burying their dead and dragging their wounded to makeshift field hospitals. For many, already pushed to the limit by fear, thirst, hunger, and exhaustion, burial duty, not combat, was the most harrowing experience of the war. The men dug mass graves and filled them with 9,000 decomposing corpses. For at least one German officer, the memory was inexpugnable, pursuing him even in his sleep long after the war: “The battles, the shooting, the freezing winter bivouacs: all those things I've long since forgotten, but not the interment of the dead at St. Privat; that was so ghastly that it still wakes me in the middle of the night.”

Bazaine meanwhile awoke from his lethargy and finished herding his broken army off the plateau of Amanvillers. Defeat and retreat seemed to enliven the marshal. In the course of 19–20 August, the 140,000-man Army of the Rhine retreated to Metz, staking out a vast semicircular encampment between Plappeville and the Moselle.

As the fighting flickered out around Mars-la-Tour and Vionville, Moltke, King Wilhelm and Bismarck, wedged between the march columns of the Saxon XII Corps, finally crossed the Moselle at Pont-à-Mousson. Prince Friedrich Karl had crossed earlier in the day and spent much of it at Gorze trying to direct the seesaw battle and its aftermath. With his usual perspicacity, Moltke grasped the larger significance of Mars-la-Tour. Bazaine was marooned, divided from the French hinterland by most of the Prusso-German army. Moltke immediately stopped the race to the Meuse and directed his IV, VII, VIII, and XII Corps to wheel into line beside Alvensleben and Voigts-Rhetz at Rezonville and Gravelotte. To reduce Steinmetz's potential for mischief, Moltke shifted VIII Corps to the Second Army and ordered Steinmetz to stand in place near Gravelotte with his sole remaining corps while the rest of the Prussian army pivoted north of him. Though hard days were ahead – Bazaine had a friendly fortress at his back and a strong defensive position – Moltke was groping for a decisive encirclement. He would either envelop Bazaine on the skirts of Metz, push him into the fortress to starve, or drive him north to Luxembourg, where, according to the laws of war, the French army would have to lay down its arms. Bazaine's thinking ran shallower; the marshal pondered until 10 p.m., when he and his general staff chief, General Louis Jarras, finally issued a dispiriting set of orders from their rooms in Gravelotte:

There were two Prussias in 1870. One was described by Theodor Fontane in Rambles through the Brandenburg March, a rambling four-volume travel book that depicted a savage Prussia still emerging from its swamps and forests. “Do not expect the comforts of the Grand Tour,” Fontane chuckled in the first volume, but “poverty, squalor and … no modern culture.” Trains were still a luxury in this industrializing kingdom of coal and iron; they plied only between the big cities and towns. For travel between Prussian villages, hired traps were needed, but they were invariably driven by resentful provincials, who would drive you round in circles, in and out of woods and streams, and end up charging you more for a short ride between neighboring hamlets than you would pay on the railway for the five-hour trip from Berlin to Dresden. Prussia in 1870 was still a “virginal wilderness,” a land of bogs and pines that ran right up to the gates of Berlin itself. It was a rough country with rough manners. The Viennese – always condescending where the Prussians were concerned – derided their northern cousins as having “two legs rooted in the Bible, two in the soil.” The Prussians could be knuckle-dragging, evangelical philistines, a conclusion that even a great patriot like Theodor Fontane was at pains to avoid.

The other Prussia was described by Karl Marx in the 1860s. Berlin, with its splendid Baroque palaces and Le Nôtre gardens, was a graceful, expanding city.

Germany exulted at the news of Sedan. Berliners illuminated the Prussian capital and sang a Te Deum in the cathedral. The phrase “German Empire” reverberated in declarations from every German state to King Wilhelm I demanding Alsace-Lorraine, financial reparations, and “that which was denied us in 1815: an independent, united German Empire with secure frontiers.” Newspapers and mayoral offices from the Black Forest to the Baltic bombarded Bismarck and the Prussian king with congratulatory reminders that Alsace and Lorraine were prerequisites for “security against French ambition and as a just reward for our national victory.” No one in Germany wished to waste the splendid opportunity presented by MacMahon's defeat and Napoleon III's capture. A popular assembly in Stuttgart affirmed that Alsace and Lorraine – German until 1582 – had to be taken back to assure the land connection between north and south Germany. Few dared speak against annexation, because any who condemned the planned seizure of Alsace-Lorraine were arrested, their newspapers seized at the printer. Bismarck's liberal gadfly, Johann Jacoby, was dragged kicking off a podium while speaking the following words: “How would the [Germans] of Posen and West Prussia approve of a victorious Poland were it to demand their annexation at the point of a bayonet?” Still, as Britain's ambassador in Berlin wryly noted, “Jacoby stands against the 40 million Germans who want Alsace-Lorraine. Bismarck has made a martyr needlessly.”

For thousands of French troops, the lacerating Prussian barrages of Sedan were just the start of their miseries.

Having voted war credits on 15 July, France formally declared war on Prussia four days later. The declaration detonated explosions of patriotic feeling in Paris. The mass demonstrations before Emile Ollivier's hôtel on the Place Vendôme, General Jean-Baptiste Montaudon nervously watched. Having declared war in the Corps Législatif, Ollivier was the man of the hour; he relished the attention, periodically appear on his balcony to wave to the surging crowds. In Paris, troops were mobbed as they marched to the eastern station. Civilian bystanders pressed in on them from all sides and joined their ranks, shouldering packs and rifles, standing drinks at sidewalk cafés, and bellowing “à Berlin! À bas les prussiens!” Citizens thronged the Tuileries Palace day and night waiting for their Napoleon to ride out and take command of the army. The French provinces were at least as excited. Troops rolling to the front in railcars recalled that even remote train stations were crowded with spectators yelling encouragement, shoving flasks of wine through the windows, and enjoining the men to rout the “German blockheads” – “têtes carrés allemands.”

French expectations ran high, and for Louis-Napoleon's troops everything turned on the speed with which they could deploy to the frontiers. Although the French would eventually be outnumbered by the Prussians, they would have several weeks in which to strike with their long-service regulars before Prussia could collect its reserves.

After Wissembourg, General Abel Douay's battered division – now commanded by General Jean Pellé – had reeled away to the southwest in the direction of Strasbourg. After pulling itself together on 5 August, Crown Prince Friedrich Wilhelm's Third Army moved off in Pellé's baggage-strewn wake. Having lost contact with MacMahon, the Prussian crown prince wanted to scour the ground east of the Vosges before turning into the mountains to join the Prussian First and Second Armies on the other side. To do this, he made a difficult change of front southward: the Bavarian II Corps scrambled down the road to Lembach on the right, the Prussian V Corps and XI Corps descended on Woerth and Soultz in the center, and the Württemberg and Baden divisions – commanded by the Prussian General August von Werder – moved up on the left at Aschbach.

The roads were difficult with ascending ranges of wooded hills that only occasionally opened on to fields of corn or tobacco before the woods or vineyards closed in again. At first, the crown prince and his staff chief, General Albrecht von Blumenthal, assumed that MacMahon was running for cover in the fortress of Strasbourg. Late on the 5th, however, a Totenkopf hussar rode through Woerth, noted barricades on the road to Froeschwiller, dismounted, swam across the Sauer, had a long look at MacMahon's sprawling position, and galloped back to headquarters.

By the first week of August 1870, Napoleon III had come under massive pressure to launch an offensive. This was not only the right thing for a Bonaparte to do politically, it was the only way strategically for France to preempt Prussia's superior numbers and organization, and, as Gramont continually reminded Leboeuf, the only way for France to lure the wary Austrians, Italians, and Danes into a French alliance. The problem, of course, was that France's advantage in the early stages of a Franco-Prussian war was presumptive and based on nothing more solid than the assumption that a larger peacetime army (France's) could mobilize more quickly than a smaller one that needed reserves (Prussia's). As it chanced, Moltke's army – regulars, reserves, and Landwehr – defeated that particular assumption, mobilizing faster than the French, absorbing Louis-Napoleon's half-hearted push across the Saar, and then swarming past it to crack the defensive French positions at Wissembourg, Froeschwiller, and Spicheren and push into France.

Truth be told, offensive operations were the last thing that the French ought to have been contemplating in the first week of August 1870. The synchronization of Gramont's bellicose foreign policy and the army's mobilization had been so utterly neglected that superhuman exertions were now required just to deploy the French army. On 1 August, eleven French guardsmen died of heatstroke marching from Nancy to Metz.

Marshal Edmond Leboeuf, France's war minister in 1870, would himself have winced at the task set him by Gramont and Ollivier. In 1870, the fully mobilized Prussian army would number more than a million men. Against this armed horde, the French would be lucky to amass 400,000 troops. The reason for the disparity was the differing mode of recruitment in Prussia and France. Whereas the Prussians relied on universal conscription – raking every able-bodied twenty-year-old into the army for three years, then releasing him into the reserves for four additional years and the Landwehr or national guard for five more – the French preferred long-service, professional soldiering, employing no reserves and recruiting fewer men but keeping them longer with a seven year hitch and bonuses for reenlistment. The two systems could not have been more different. Fifty percent of the French army in 1870 had served seven to twenty-one years on active duty.

The Prussians were greenhorns by comparison. Indeed with its short, compulsory service, the Prussian army was essentially a training school for the reserves, ratcheting a relatively small peacetime strength of 300,000 up to 1.2 million with the call-up of 400,000 reservists and 500,000 Landwehr. The chief defect of the Prussian system was its relative amateurism; the officers and NCOs were the only career soldiers in the army, which made it difficult to build an expert reserve and train new formations.

As the French reeled away from Beaumont in the direction of Sedan, where Marshal MacMahon hoped to find a temporary refuge, Moltke scribbled orders for 31 August: The Meuse Army would march down the right bank of the Meuse, extending its right wing all the way to the Belgian border; the Third Army was to surge ahead on the left bank to Sedan, seize whatever bridges it could, begin crossing, and push troops into the space between Sedan and Paris. While Moltke worked, so did Bismarck, reminding Brussels of its obligation to disarm and intern any French troops that crossed the Belgian border. If the Belgians permitted the French to regroup on their neutral territory, the Prussians would invade. By late on 31 August, a French withdrawal to Belgian soil had become all but impossible anyway, for the Saxons and the Prussian Guards had extended themselves north and east of Sedan, the Prussian 6th Cavalry Division north and west at Mézières. South of Sedan, the Bavarians had advanced to Bazeilles, Wadelincourt, and Torcy, the Prussian IV Corps to Frénois, the Prussian XI and V Corps to Donchéry, enabling Moltke to push vanguards across the Meuse to block MacMahon's escape in every direction and begin the famous Umgehung or envelopment. French engineers sent from Sedan to blow up the Donchéry bridge discovered that all of their gunpowder and blasting caps had been evacuated to Mézières; scouring Donchéry for replacements, they were chased off by Prussian skirmishers.

On 3 July 1866, even as Emperor Napoleon III made plans to dispatch an envoy to Prussian royal headquarters to urge restraint, a quarter of a million Prussian troops under the command of General Helmuth von Moltke smashed the Austrian army at the battle of Königgrätz. In just three weeks of fighting, Moltke had invaded the Austrian province of Bohemia, encircled Prague, and punched the Habsburg army into a loop of the Elbe river between the Austrian fortress of Königgrätz and the little village of Sadova. There Moltke nearly annihilated the Austrians, killing, wounding, or capturing 44,000 of them and putting the rest – 196,000 largely disbanded stragglers – to panic-stricken flight.

Königgrätz was a turning-point in history. Prussia's fifty-one-year-old prime minister – Count Otto von Bismarck – watched the battle at Moltke's side and offered the Austrians terms, when the extent of their defeat was fully comprehended in Vienna and elsewhere. In exchange for an armistice, Emperor Franz Joseph of Austria duly surrendered the authority his Habsburg dynasty had exercised in Germany since the sixteenth century, first through the Holy Roman Empire, then through the German Confederation, and gave the Prussians a free hand. Bismarck was quick to exploit it. In the weeks after Königgrätz, he abolished the thirty-nine-state German Confederation established in 1815 and annexed most of its northern members: Schleswig, Holstein, Hanover, Hessia-Kassel, Nassau, and Frankfurt-am-Main.