The Estates-General was a key event in the French Revolution. This began as a meeting of the "three estates" of French society (the nobility, clergy, and peasantry) to try and solve the issues troubling the nation. The government was in extreme debt due to their involvement in a number of wars and several years of crop failure. The peasant class (called the third estate) had been angered by the rise in prices of bread, which exacerbated pre-existing tensions between the land-holding nobility and the laborers who worked the land.
At the Estates-General of 1789, conflict arose when the three estates could not decide how to vote. If the Estates were to vote independently of one another, it would give an advantage to the nobility and clergy, who made up a relatively small part of society. If the three were to vote all together, the votes of the peasantry were sure to overpower the nobility and clergy. Naturally, the nobility were reluctant to let their decision-making power be overwhelmed by the laboring class!
When a solution to the dispute over voting could not be achieved, the representatives of the Third Estate formed the National Assembly with the intent of solving France's problems with the peoples' interests at heart. They invited the other two Estates to join, and though the King initially resisted, the nobility and clergy eventually had no option but to join the National Assembly. The peasant class could easily have overpowered the First and Second Estate, so resisting did not make much sense.
Later that year, the combined Estates (now known as the National Constituent Assembly,) would pass the Declaration of the Rights of Man and the Citizen. This document effectively put an end to the feudal system (and rule by nobility) in France, promoting the values of equality, liberty, and brotherhood for all.