A large part of the action of the Commune was to fight against the offensive led by the troops of the government of Thiers:the "Versaillais".
As evidenced by the telegraphic correspondence he had with Jules Favre, who was negotiating peace with the Germans, Thiers enjoyed the support of German Chancellor Bismarck. It is indeed a question of putting an end to the hostilities between France and Germany as soon as possible, one of the conditions being the disarmament of Paris. While the armistice agreement only authorized 40,000 French soldiers in the Paris region, Bismarck quickly released nearly 60,000 prisoners of war who could join the 12,000 soldiers available to Thiers. On April 1, Thiers confessed to the National Assembly that he was setting up "one of the finest armies that France had possessed". The Versaillese will be 130,000 at the start of the Bloody Week. These soldiers of a professional army (7 years' service) are mainly from the peasant background. The review boards dismissed most young people from the cities for "physical deficiency", because of the working conditions that the industry of the time imposed on young workers, despite the 1841 law on child labor. They are commanded by the vanquished of Sedan, Marshal de Mac-Mahon. In the northern and eastern "suburbs" of Paris, which they controlled, the Germans let the Versaillese troops who wanted to bypass Paris pass. In addition, the Germans, by agreement with the Thiers government, occupied the Chemin de fer du Nord, established a barrage of troops from the Marne to Montreuil and massed 80 guns and 5,000 soldiers near the Porte and the fort of Vincennes (held by the Communards) thus blocking the eastern exit of the capital.
Faced with this numerous, experienced and well-armed army, the Commune had the men of the National Guard at its disposal. Since the Restoration, all men aged 25 to 50 with their political rights are part of it. The weapons are provided by the State, but the clothing remains the responsibility of the guard. In Paris, recruitment is done by district. Within the communal limits the service is free, but the guard receives a pay if he serves beyond. Under the Second Empire, all married men between the ages of 25 and 50 were enlisted. On August 12, 1870, the government reorganized 60 battalions. The bourgeois districts of Paris (the west and the center of the capital) provide more than three quarters of it. At the beginning of September the government of National Defense created 60 others, at the end of September there were 254 battalions! Three-quarters of the new creations come from working-class neighborhoods in eastern Paris (10th, 11th, 18th, 19th and 20th arrondissements). We can see the influence of the siege of Paris by the Germans which revives the patriotic fiber of the Parisians, but also the hope of receiving the pay, which has become the only income of working-class families affected by unemployment following the blockade of Paris by the Germans. On April 5, the Commune decreed the mobilization as volunteers of young people aged 17 to 19 and in compulsory service of single men and married men aged 19 to 40. These men have practically no military experience and if they are animated by a republican ardor are rather reluctant to discipline and suffer, despite some notable exceptions (Dombrowski, Rossel), from a lack of command (the officers are elected more on their convictions than on their ability to lead soldiers). In theory the Commune has nearly 194,000 troops, non-commissioned officers and officers (number published by the Official Journal of the Commune on May 6). In fact, the combatants are fewer. Estimates range from 10,000 (Camille Pelletan) to 41,500 (Cluseret, War Delegate, April 5). They can be estimated at 25-30,000 at the beginning of April and half as many in mid-May. The haemorrhage can be explained by the fact that many registered are there only for the pay and remained spectators during the fights; without counting those who perished in the military operations against the Versailles troops.