Robespierre Denounced France's war against Austria (1792) on the grounds that France was not prepared for a conflict of this magnitude. He was part of the National Convention, which was elected by universal suffrage, and in which he sat among the mountaineers, named for having their seats in the upper part of the Chamber of the National Assembly. The support of the revolutionaries of Paris (the sans-culottes) in the assemblies of each district and municipality of the Parisian region, brought Robespierre to power: first as a member of the revolutionary Commune (the city council) that held the local power; then as representative of the city in the National Convention that assumed all the powers, and in which Robespierre appeared as spokesman of the Radical party of the Mountain (along with Danton and Marat). It was at this time that Robespierre openly manifested his republicanism. He fought firmly against the Girondins, the group of moderate deputies from the Bordeaux region, the Gironde, a conservative group that advocated a decentralized state and was inclined to maintain the constitutional monarchy or, in any case, carry out a revolution moderate Earlier, Robespierre disagreed with the Girondins on the advisability of war against the European monarchies, which the Girondins defended with the argument of bringing freedom to the subjects of the kings. Robespierre was against it, convinced that "nobody wants the armed missionaries". The Girondists constituted a very strong political pressure group in the National Assembly but when opposing the line of radical republican firmness represented by the Jacobins and after their rejection of the execution of Louis XVI (which they considered excessive), Robespierre did not stop attacking them savagely in his speeches. Finally, in 1793, Robespierre, supported by a popular masses suitably directed, gave a coup d'état and dismantled the Girondin group, arresting all the main leaders he could capture.
The period of the Terror supposed the death in the guillotine of thousands of people, many of them workers and peasants, but above all it was a symbol of total rupture with the absolutist past and the monarchy. Robespierre had been a strong supporter of the abolition of the death penalty, but his perception was modified by assuming the obligation to defend the Republic from his enemies, coming to consider that it was justified, as long as the executed was an "enemy".