How did the Reign of Terror turn on the revolutionaries who made it?

The Reign of Terror was the period of the Revolution, after the First Republic was created, when a series of massacres and numerous public executions took place. By July 1794, 16,594 official death sentences had been issued across France since June 1793, 2,639 of them in Paris, and an estimated ten to twenty thousand more people were executed without trial or died awaiting trial in prison. It turned on its own makers when, as the Terror accelerated, members of the Convention felt more and more threatened and began to plan the overthrow of Robespierre.

Historians disagree about when exactly the Terror began. The Convention agreed to a revolutionary army in September 1793 but refused to make terror the order of the day. Albert Soboul summed up its logic: terror, at first an improvised response to defeat, became an instrument of victory once organised. Robespierre defined it in February 1794 as nothing more than speedy, severe and inflexible justice. The Law of Suspects, passed on 17 September, authorised the imprisonment of vaguely defined "suspects" and overfilled the prisons.

The key turn came in 1794. By the end of 1793, the Hébertists wanted to intensify the Terror, while the Dantonists demanded moderation and clemency; the Dantonists were executed on 5 April. Then on 10 June came the Law of 22 Prairial, the law of the Great Terror. It barred the Tribunal from calling witnesses or allowing defence counsel, and left only two verdicts: acquittal or death. Executions rose from five a day to seventeen and then twenty-six.

On 9 Thermidor (27 July 1794) the conspiracies against Robespierre came together, and the Convention declared the Robespierrists outlaws, meaning they could be executed within 24 hours without a trial. Taken the next morning, 28 July, Robespierre was executed that same day with 21 of his associates. The irony: as a young lawyer, Robespierre had resigned as a judge because of his opposition to the death penalty.