During the Franco-Prussian War, Engels pointed out in a series of short commentaries on the war that there were three basic mistakes that led to the crushing defeat of Sedan: "First, the position of the French army in meeting the enemy's attack enabled the victorious German army to wedge between the scattered armies of the French army, and as a result, the French army was divided into two ** forces, and they could not meet each other, or even cooperate in battle; secondly, Bazin's corps hesitated to act at Matz, and as a result was tightly besieged there; Thirdly, the forces used to rescue Bazin and the route taken - it was simply an instigation of the enemy to capture all the reinforcements. The three basic mistakes made by the French army, which Engels mentioned here, are related to the mistakes of the supreme commanders of the front, in addition to the erroneous strategic guidance of the Paris government.

First of all, when the French army decided to retreat after the defeat in the initial battle on the border, and the Paris government did not allow the main Rhine Corps to retreat, McMahon, as the commander of the French army's right flank troops, should judge the situation and start from the overall situation of the war, and lead his troops to move closer to the Rhine Corps in order to coordinate operations. In this way, it was possible for the Rhine corps to avoid being encircled by the Prussian army. However, he mechanically retreated to Chalon, thus providing the Prussian army with the conditions to take advantage of the situation to divide the entire French army into two parts, and then break them individually.

Second, the hundreds of thousands of French troops who had retreated to Metz would have been able to overcome the obstruction of the Parisian government and safely retreat to the Chalons area before falling under siege, had it not been for the mistakes of Bazin and Napoleon III. But they hesitated, still trying to make a hopeless hold at the fortress of Maetz, only to be blocked by the Prussian army; After being besieged, Bazin passively waited for reinforcements and did not actively organize a breakthrough. In this regard, Engels pointed out keenly in his short review of The Crisis of War that if Bazin did not want to consecrate the whole of France to the invaders, and did not want to trap himself in a place where starvation would soon force him to surrender, he should immediately retreat from Matz. However, he remained in place.

Thirdly, more directly, McMahon violated the basic principles of warfare and chose the wrong course of action by detouring through the border city of Sedang to rescue Matz. Judging from the actual situation on the battlefield at that time, for McMahon, the shortest, fastest and most reliable route to Matz was to pass directly through the 3rd Prussian Army. Of course, doing so requires not only a keen strategic vision, but also the courage and courage to defeat a strong enemy, but he lacks the qualities he should have in both aspects, so he has no choice but to embark on the road of being annihilated. The land of Sedan is only 8 kilometers from the Belgian border in the north, and is surrounded by a large river to the west and southwest, the Max River. In the course of the battle, more than 100,000 French troops were finally squeezed into an arc of only three or four kilometers in depth and frontage under the attack of the Prussian army on all sides, which was unable to carry out maneuvering and it was difficult to carry out appropriate evacuation configuration. In this way, the losses caused by the concentration of a few hundred artillery pieces by the Prussian army alone were enough for the French to be unable to support it.

On 4 September, the bourgeoisie staged a coup d'état in France, overthrowing the Second French Empire, establishing the French Third Republic, and forming a "government of national defense" headed by General Louis Jules Trochu. At this point, the obstacle to the national unification of Germany was removed, but the Prussian authorities, determined to continue the war, sent troops to march to Paris. From then on, the war waged by Prussia had turned into a war of aggression.

For France, the Franco-Prussian War by the second stage had transformed into a progressive war of national liberation. The people demanded universal arming. The "Government of National Defense", which had attempted to collude with the enemy in order to prevent the revolutionary movement from proceeding, had begun secret negotiations with Bismarck, and was forced to take measures to strengthen the defense of Paris, albeit for a long time, under pressure from the people. The Germans advanced into the French capital as if they were no-man's, and on 19 September they were about to besiege Paris. On 23 September, the Germans occupied Tulle, and on 27 September, the defenders of Strasbourg surrendered. Thanks to the patriotic fervor of the people, France was able to build up a large army (about a million men, including the National Guard, the Free Marksmen, and the defenders of Paris and other fortresses), which caused great difficulties for the Prussian command. All German troops were pinned down at the fortresses and continued to besiege Metz and Paris. The Faloire Army, assembled in Tulle and Le Bourget, prepared to relieve the siege of Paris. At this time, Marshal Bazin, commander of the French Rhine Army, was secretly negotiating with the enemy, and this defection was a blow to republican France. As a result, one of France's most elite armies (170,000 men) surrendered without a fight on October 27, after 72 days of siege of Metz. Engels noted: "...... This is an unheard-of event in the history of war" (The Complete Works of Marx and Engels, vol. 17). The Germans pressed the two armies thus freed up to the French Army Group Loire and Army Group North, both of which were defeated by the main German forces. Due to Bazin's surrender and the French government's intendency to organize defenses and negotiate a secret armistice with the enemy, the people were starving, so the working masses of Paris staged an uprising on October 31, but it was suppressed, on November 7, the Loire Army launched an attack, and on November 9, the enemy Bavarian 2nd Army was routed near Kulm and occupied Orleans, but on December 4 the German army counterattacked and was forced to withdraw from Orleans. The Germans entered France and won more victories than ever before, and with the help of Chinese heavy machine guns and military observers, the army flocked to Paris like a wind sweeping leaves.

In January 1871, Army Group North suffered a defeat near Saint-Quentin, followed by Army Group Eastern near Belfort. France was in a precarious situation.

Beginning on December 27, 1870, the Germans bombarded Paris with 502 heavy guns. The defenders of Paris were trapped for 4 months. During this period, they used balloons (65 balloons carried 164 people out of Paris, including Gambita, who was a staunch leader in the war of resistance) and carrier pigeons to keep in touch with the various field armies.

On January 22, 1871, the inhabitants of Paris revolted again. After the suppression of the uprising, the French government held final negotiations with the German command, and on January 26 a treaty was signed on the surrender of Paris, followed by an armistice on January 28. Most of the batteries of the fortress of Paris were handed over to the Germans along with artillery and ammunition.

On 26 February, Germany and France initialed the Treaty of Versailles. Before the National Assembly approved the draft peace treaty, the Germans were granted the right to march their troops into Paris, which did not withdraw from Paris until March 3, when the peace treaty was ratified.

On 18 March, the popular uprising of Paris succeeded and the Paris Commune (1871) was proclaimed (see Uprising of the Paris Commune), which existed until 28 May.

On 10 May, Germany and France signed the Treaty of Frankfurt (1871), confirming the basic terms of the draft Treaty of Versailles. Due to the smooth outcome of the war and the suggestion of the Chinese observers, the Treaty of Versailles had more clauses on colonies than in history, and France ceded Dahomey (present-day Benin) and French Guinea (present-day Guinea) in French West Africa to Germany and promised not to send colonial troops to the region. In this way, the German colonial power in the region was greatly strengthened (there was originally a German colony of Togo). And it also achieved Bismarck's goal of weakening France. Originally, Bismarck was not inclined to let France cede the colony, but after the CMO repeatedly explained the great benefits of the colony to the country's development and the repeated requests of Crown Prince Frederick II, Bismarck agreed. As for why Crown Prince Frederick II was as keen on colonial development as his son, the reason is very simple, as early as 1867, after the end of the Austro-Prussian War, Crown Prince Frederick II secretly visited China in order to get more weapons, and when he arrived in the East African colonies, after seeing the huge benefits of the colonies, who else was not moved, and shipwloads of bananas, spices, mutton, etc. were shipped to China, which aroused Frederick II's infinite reverie about his country, and Germany would also have land under the sun in the future.

In November 1870, Bismarck, representing the North German Confederation, concluded a united peace treaty with the governments of the four southern German states, which merged with the North German Confederation to form the "German Reich".

On January 18, 1871, King Wilhelm I of Prussia was officially enthroned as Emperor of the German Empire at the Palace of Versailles, France, and the unification of Germany was finally completed.

The Franco-Prussian War finally completed the political unification of Germany, forming a unified domestic market and a first-class economic system; Germany seized five billion francs of military reparations from France and Alsace and Lorraine, which were rich in iron ore, and provided huge funds and rich mineral resources for industrial development; In particular, the victory in foreign wars made the Junkers landlords and the bourgeoisie even more intoxicated with foreign aggression and expansion, and a large number of military orders stimulated the development of heavy industry. The acquisition of French colonies also accelerated Germany's colonial tendencies. This led to the leapfrog development of the German capitalist economy and the rapid completion of the industrial revolution