What conditions led to the reign of terror, and how did the committee of public safety defend its brutal actions against the people?

The Reign of Terror was a dark chapter in the French Revolution because it resulted in the deaths of thousands of people.  Leopold III Emperor of Austria and King Frederick William II of Prussia wanted to help Louis XVI and this resulted in the Declaration of Pillnitz on August 1791 declaring their intention restore the French monarchy back to power. The French people were angry with this and they raised an army that repulsed the invaders. Because many French emigrants persuaded were trying to get support to restore the monarchy.  Suspicion grew and with it came the Committee for Public Safety whose job was root out those who supported the monarchy.  They did so through violent means as many people were killed.  Through suspicion alone, it gave them the right to kill anyone they thought was against the new government.  They justified their actions by saying many had to die to protect the Revolution.  Still it was wrong because many were killed without the right to a fair trial.