Following the Treaty of Frankfurt and France's loss in the Franco-Prussian War, on 18 March the new French government under Prime Minister Adolphe Thiers attempted to remove a large number of cannon from a park in Montmartre, to keep them out of the hands of the more radical soldiers of the Paris National Guard.

In April, the Commune launched a military expedition against the Versailles government led by Gustave Paul Cluseret, who had fought with Giuseppe Garibaldi and had been a general in the Union Army.

The National Guard came under fire from Fort Mont-Valérien, broke ranks, and fled back to Paris pursued by the French Army.

Soldiers suspected of sympathies to the Communards were transferred to other regiments, and often sent to French outposts in North Africa or regions distant from Paris.

On 20 May, a concert was held in the Tuileries Garden to raise funds for widows and orphans, though the Versailles artillery could be heard from the army positions outside the city.

[17] On the afternoon of Sunday, 21 May, despite the sound of artillery bombardment from the Versailles batteries outside, a charity concert to raise funds for orphans and war victims went ahead in the Tuileries Garden, and attracted some eight thousand people.

General Félix Douay telegraphed Marshal MacMahon and the high command, and the army immediately began moving troops through the gap into the city.

The wide boulevards were not conducive to defensive urban warfare, while the decentralized nature had no structure for joint action between the forces of the different neighborhoods.

Tribunals met at the Ecole Militaire, Parc Monceau, the Luxembourg Palace, Place Vendôme, the Gare du Nord, the city halls of the First and Fifth Arrondissement, the Panthéon, the École des Arts et Métiers, and other locations,[33] Following their trials, those who were sentenced to death were taken immediately to nearby execution sites; these included the construction site for the Gare du Nord, the esplanade in the Tuileries Garden the Luxembourg Gardens, Place du Châtelet, the Mazas Prison and later, as the army moved east, the Père Lachaise Cemetery.

[34][35] The Polish nobleman Jarosław Dąbrowski was a senior military commander of the Commune, but rumours had spread that he had received a large bribe in exchange for surrendering the city to the Army.

At ten o'clock in the evening, a group of Commune officers escorted Dąbrowski to the Hôtel de Ville to turn him over to the Committee of Public Safety.

By the end of the day, the army effectively controlled half the city, along a line from Montmartre in the north to Parc Montsouris in the south.

"[36] In the evening the National Guard adopted a new tactic; they began setting fire to the government buildings they still controlled, beginning with the Tuileries Palace.

[36] Early in the morning on the 24th, the Commune leaders abandoned their headquarters at the Hôtel de Ville and moved to the city hall of the 11th arrondissement.

National Guard soldiers began preparing a bonfire inside Notre-Dame de Paris to burn the cathedral, following the example of the Tuileries Palace and other government buildings.

They proposed the dissolution of both the Commune and the National Assembly, the withdrawal of the army from Paris, the election of new governments in the large cities, and a general amnesty.

[38] A delegation led by Gustave Genton, a member of the Committee of Public Safety, went to the new headquarters of the Commune at the city hall of the 11th arrondissement and demanded the immediate execution of the hostages at the prison of La Roquette.

Instead of attacking the barricades directly, the French Army spread out and worked their way through the narrow streets around it, tunnelling through walls and outflanking the Commune positions.

The National Guard created a distraction by setting fire to the Gobelins tapestry factory, but the Versailles soldiers bypassed the barricades by moving through neighborhood gardens.

[42] At about 7:30 in the evening, Delescluze put on his ceremonial sash as the chief executive of the Commune and walked to the barricade at the Place Château d'Eau.

[42] During the night of 25–26 May, the Versailles army occupied several strategic points abandoned by the Commune, including the barricade on Rue Saint-Antoine, the Gare de Lyon railway station, the Mazas Prison, the Square du Temple, and boulevard Voltaire.

[43] At six in the evening, sixty-two or sixty-four hostages including clergymen and thirty-four gendarmes were collected by the Commune and brought to Rue Haxo near Belleville.

The National Guard still had a rectangle of barricades defending La Villette, Belleville, Menilmontant and Charonne, and controlling the grand boulevards.

The wide boulevards built by Napoleon III gave the National Guard an advantage by creating clear lanes of fire.

[48] Fighting continued around Belleville and Menilmontant and near Père Lachaise into the night of 27–28 May, but by the morning, the French Army had encircled National Guard forces by moving around the city walls, trapping the remaining soldiers.

The remaining Commune leaders were all trapped within this pocket: Jules Vallès at the bottom of Rue de Belleville, and Eugene Varlin and Theophile Ferré at the Faubourg-du-Temple.

The Second Division of the Fifth Corps of the French Army lost three soldiers on 22 May; six on 23 May; four on 24 May; then sixteen on 25 May, when they attacked the strong defenses of the Arts et Metiers quarter; three on 26 May, one on 27 May, and one on 28 May, the last day of combat.

[52] The wall of Père Lachaise where Communard soldiers were executed is now marked with a plaque to the victims of the Semaine sanglante, and is the site of annual commemorations of the event.

[54] Historian Robert Tombs concluded that a majority of the Communards that were killed were shot by firing squads after brief trials by military courts around the city.

[57] It is estimated by more recent historians, based on cemetery records, to be between ten and fifteen thousand, with the possibility, if more graves or evidence is found, of being higher.