Final answer:
The Reign of Terror concluded with the execution of Robespierre and his associates after he was accused of treason by the National Convention. This event led to a shift towards conservatism and the rise of Napoleon Bonaparte, who later crowned himself Emperor.
Step-by-step explanation:
The Reign of Terror ended with D) the execution of Robespierre and his colleagues. Maximilien Robespierre was central to the Committee of Public Safety, which employed the Terror as a means to maintain the revolution. The Law of 22 Prairial allowed for rapid executions via the guillotine, a symbol of the era's violence. By July 1794, following increased internal executions without discernible external threats, the National Convention accused Robespierre of treason. His attempted death failed, and he was subsequently executed, marking the end of the Terror.
After this period, France experienced more conservative governance under the Directory which was ultimately overthrown by Napoleon Bonaparte, declaring himself Emperor and ruling an extensive empire. While Napoleon upheld certain revolutionary advances, he also reversed some changes like reinstating slavery in colonies and establishing an authoritarian regime.