In what ways did the end of the old order move the revolution toward a more radical phase?

Robespierre became in control and the Reign of terror took place

Maximilien Robespierre was one of the main figures behind the execution of King Louis XVI, which marked the end of French's monarch system. Robespierre believed that without the radical phase, there is no way the French nobles would pay attention in any way to the voices of the commonfolk.