Volumes and volumes have been written about this and it would be impossible for us to give you an answer in the small space that we are allowed here. You must do some research on it, but I will try to give you some direction.
The world-wide revolutions that took place in the 1700s and into the 1800s and 1900s (1917 - Russian Revolution) were sparked by the ideas of the Enlightenment (liberty, equality, brotherhood, rights of man, etc.) So, too, with the French Revolution. The French were encouraged by the success of the American Revolution in 1776, but the French situation was much different and therefore, the French Revolution turned to terror. There was very little moderation, except at the beginning, and it was such a mess that a strong leader was required to come in and clean up the mess (Napoleon = empire).
The French monarchs (Bourbon kings - the Louis kings) had been prone to excesses for years and years and years and the French people suffered on all levels, not just on a political level. The French Revolution was all encompassing - it was a social revolution as well as a political one. The people were miserable and starving, on top of being politically oppressed. There were several groups that had control that were made up of radicals, and this led to the Reign of Terror. The outcome of this revolution was quite different than in the United States.
This is a very over-simplified answer, but if you do some research, you will find the specifics you need.