In 1789, an Estates-General was recommended by the nobility and agreed to by the French King Louis XVI. The Estates General was composed of three bodies; the First Estate (the French clergy), the Second Estate (the nobles), and the Third Estate (mostly constituted by lawyers). For centuries, each of the Estates were given one vote. Each Estate voted within itself and then presented its vote against the votes of the other two, and if a proposition had two out of three votes in its favor then it would pass. Often times the Third Estate was outvoted by the other two Estates. It felt that this was unfair, since the Third Estate didn’t just represent a mere third of the nation but by far the majority. And so the Third Estate sought to have a resolution passed giving each estate a fair vote for the people it represented.
Eventually, after being allowed to have more delegates but the same one vote, the Third Estate separated itself from the rest of the Estates-General, and set itself to creating a French Constitution. Though the King actually agreed to this move and ordered the other estates to join the Third, a guard of soldiers had set up post in front of their usual meeting house and refused to let them enter. Believing that this was a sign of the King turning against them, they took an oath together to never quit until they had given France a new constitution. This event is known as the Tennis Court Oath, and was a major turning point in the French Revolution.
Following this turn came a series of principles and ideas, many taken from the American Revolution, though not always in its pure form. The rights of the people were supported, the abolishment of the feudal system, and many other changes were proposed.
However, this mostly peaceful Revolution took a violent turn. After raiding the Bastille, a frenzied populace killed the French King and then set up the Committee of Public Safety. This body eventually led by Maximilien Robespierre killed thousands by drowning, the guillotine, the sword, bayonet, etc; this period being popularly known as the Reign of Terror.