During the war, the Paris National Guard, particularly in the working-class neighbourhoods of Paris, had become highly politicised and units elected officers; many refused to wear uniforms or obey commands from the national government. National guard units tried to seize power in Paris on 31 October 1870 and 22 January 1871. On 18 March 1871, when the regular army tried to remove cannons from an artillery park on Montmartre, National Guard units resisted and killed two army generals. The national government and regular army forces retreated to Versailles and a revolutionary government was proclaimed in Paris. A Commune was elected, which was dominated by socialists, anarchists and revolutionaries. The red flag replaced the French tricolour and a civil war began between the Commune and the regular army, which attacked and recaptured Paris from 21–28 May in La Semaine Sanglante (Bloody week).