The Cult of the Supreme Being.

I bet you didn't know that during the French Revolution they invented a new calendar (and the metric system..but that was a good thing)  Yes they invented a new calender, it had 12 months with 3 weeks made up of 10 days with 5 days left over as complimentary days.  They did this to dechristianize the nation.  The 10 day week was so people wouldn't know what day Sunday was.  They removed any trace of the Catholic faith from the country, including creating a new calender and renaming streets.
These ideas were brought forth by the Cult of the Supreme Being.  They realized that people need a religion to believe in, hence they created the Cult of the Supreme Being.

Maximilien Robespierre was the leader of the France at the time, this was during the reign of terror, or the great terror.  He started out as a good leader, strong man that didn't like violence.  He wanted to change France into a democratic state without an absolute ruler, without a king that taxed the poor and helped the rich.  A country where all men were equal (men, not women)  By the end, he was insane.  Really he was, thousands of people were killed under him, he thought that the only way that peace could be found was through violence.  Soviet Russia would echo this era in the future.  Suspicion was high , and you could be beheaded for anything.  He was also the supreme being that gave the cult it's name, he became bigger than the cause.  He truly believed that with out him it would all crumble.
So the Festival of the Supreme being one day no killings happened, and it was found out that a giant paper mache mountain had been built in the middle of Paris.(see painting above)  Robespierre descended from the top of the mountain draped in a toga. This is when people realized that he had gone crazy.
He was beheaded a little while later.
Like most great leaders he just got caught up with greed and hate and murder.  They wanted to save their countries, but in the end killed it's people.