In September 1870, Napoleon III surrendered to Bismarck at the border town of Sedan, less than two months after France had declared war on the well-prepared and superior forces of the Prussian state. The humiliation was enough for a Republican government to be instantly proclaimed in Paris. The Prussians advanced and by September 19 were laying siege to the capital. Gambetta was flown out by hot-air balloon to rally the provincial troops, but the country was defeated and liaison with Paris almost impossible. Further balloon messengers ended up in Norway or the Atlantic; the few attempts at military sorties from Paris turned into yet more blundering failures. At the same time, the peculiar conditions of a city besieged gave a greater freedom to collective discussion and dissent. 

The government's half-hearted defence of the city - more afraid of revolution within than of the Prussians - angered Parisians, who clamoured for the creation of a 1789-style Commune. The Prussians meanwhile were demanding a proper government to negotiate with. In January 1871, those in power agreed to hold elections for a new national assembly with the authority to surrender officially to the Prussians. A large monarchist majority, with Thiers at its head, was returned.

On March 1, Prussian troops marched down the Champs-Élysées and garrisoned the city for three days while the populace remained behind closed doors in silent protest. On March 18, amid growing resentment from all classes of Parisians, Thiers' attempt to take possession of the National Guard's artillery in Montmartre set the barrel alight. The Commune was proclaimed from the Hôtel de Ville and Paris was promptly subjected to a second siege by Thiers' government, which had fled to Versailles, followed by all the remaining Parisian bourgeoisie.

The Commune lasted 72 days - a festival of the oppressed, Lenin called it. Socialist in inspiration, it had no time to implement lasting reforms. Wholly occupied with defence against Thiers' army, it succumbed finally on May28, 1871, after a week of street-by-street fighting, in which three thousand Parisians died on the barricades and another twenty to twenty-five thousand men, women and children were killed in random revenge shootings by government troops. Thiers could declare with satisfaction - or so he thought -"Socialism is finished for a long time."