Well, there were several causes of the Reign of Terror. There were some external threats, which included the war with Austria and Prussia, and the fact that European monarchs were angry over the death of King Louis XVI. Then, some internal threats prevailed, such as leaders Maximilen Robespierre who used the guillotine to kill political rivals and "traitors." Really, almost anyone in France were at risk of dying: men and women, rich and poor, high ranking politicians, lowest criminals all could be swept up and executed if they disagreed with Robespierre's ideologies