Prior to the Civil War?

From Wikipedia today
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The Cato Street Conspiracy was an attempt to murder all the British cabinet ministers and Prime Minister Lord Liverpool in 1820. The name comes from the meeting place near Edgware Road in London.

Origins of the conspiracy
The conspirators were members of a group of Spencean Philanthropists, named after the British radical speaker Thomas Spence. Some of them, especially Arthur Thistlewood, had been involved with the Spa Fields riots in 1816. Thistlewood came to dominate the group. Most of the group were angered by the Six Acts and the Peterloo Massacre, as well as with the economic and political depression of the time. The plan was to assassinate a number of cabinet ministers, overthrow the government and set up a Committee of Public Safety to oversee a radical revolution, similar to the French Revolution. According to the prosecution at their trial, they had planned to form a provisional government headquartered in the Mansion House.