On January 21, 1793, King Louis XVI of 
France was executed. Image: Isidore-Stanislas Helman, The Death of King Louis (1794), Bibliotèque nationale de France (click for geospatial location). This work is in the public domain in the United States.
1793 was a key juncture in the revolution, beginning with this execution on 21 January. The increasing violence prompted Britain to cut its ties to France, leading to declarations of war by the two countries. Violence peaked during the Reign of Terror (5 September 1793 – 27 July 1794), which resulted in the execution of the Queen (16 October) as well as of many suspects of treason and members of the Girondins, the more moderate faction that the radical Jacobins brought down on 2 June 1793
Articles
Diane Piccitto, “On 1793 and the Aftermath of the French Revolution”
