Medieval origins and history of the French nobility
As a social class the French nobility descended straight from early medieval times. At that time the sovereign had no possibility to organise the finance of a standing army, and therefore designated part of his population to fight for him. This was done by giving out fiefs. In this feudal construction the king was lord of the land and his vassal held it from him. In turn this vassal could have other vassals. All these vassals were to support themselves from their fief and to appear when the king called them to arms
A fief was a lordship (seigneurie) over a piece of land. As seigneur of the fief the nobleman could give out a part of it to other vassals, could give out a cens (kind of everlasting tenancy) to a farmer and had to reserve a part under his direct dominion. The rent that he got from the farmer for a tenancy was often one or two sous for an arpent (about 0.5 Ha) of land. Which amounted to a substantial part of the income that the farmer generated.
This assistance given to the king was given in armour and on horseback, and accompanied by henchmen. In this way the king could rely upon an army of thousands of armoured horsemen in times of war, and in times of peace these fended for themselves. Though the initial creation of the nobility of course did not take place in the aforementioned fashion, the numbers of the nobility were certainly kept up by the sovereign creating dukes, counts, barons etc. etc. throughout medieval times. For a long time the combination of the technique of warfare and the organisational status and wealth of the kingdom simply did not allow another way of financing a standing army of the same numbers and quality.
The French nobility during the rennaisance
During the rennaisance certain factors diminished the necessity of having this kind of a nobility. The advent of the firearm and the pikeman meant that the armoured knight did no longer have absolute rule on the battlefield. A body of well organised pikemen and musketmen could resist the onslaught of a body of armoured knights, and was a lot cheaper to acquire and maintain. During the renaissance states had also grown stronger and wealthier, and were better able to temporarily hire companies of mercenaries.
From about 1250 till 1700 the sous that the nobility got for their cense was debased till it was worth only a few percent of the medieval coin. This threatened to bring about the financial ruin of the lesser nobility. Even in medieval times fiefs had been sold to civilians, and this started to increase. Those noblemen who had enough money or influence started to buy and take back their censes, but not all succeeded in this. From about 1500 inflation began to play its role as all prices started to rise due to the influx of precious metals from the Americas.
The tendency to exclude the nobility from the administration and the staggering amount of civil war during the reformation also didn't increase the fortunes of the nobility. The feudal rights of the nobility were also getting limited by the courts. Fact is that by about 1650 most of the lesser nobility had lost its economic ability to exist comfortably. At the same time the aristocracy did succeed in getting along and retaining its power base.
There thus was little military reason left to have a feudal nobility by 1650. The French nobility did however still retain some of the feudal rights, and was used to waging war. It also had strong local ties that enabled them to ally themselves with local communities. When the population was heavily pressed by the government of Cardinal Mazarin it revolted in 1648, a revolt called the 'Fronde'. In this short civil war the nobility sided partly with the revolt, and partly with the court, and Mazarin saved himself only by his cunning. For Louis XIV it would be a permanent reminder to watch out for the nobility.
The tamed nobility
While Cardinal Mazarin had already done a lot to centralise authority in France Louis XIV would continue his work. He would do this by constraining the upper nobility to live at his court in Versailles. There he entertained them with games and plays and all kinds of amusement. These had to take there thoughts away from waging war and comply them to spend much more than they had. This in turn made them dependent on royal favour for their income, and brought them into a state of submission to the king.
The lesser nobility stayed in the country and had to devise ways to make ends meet. By law its options were however limited to investments, wholesale trade or a military career. If a nobleman did not have money to start out this practically meant a military career. A military career could bring huge profits and as a ground rule officer appointments were reserved for the nobility. The real profits were however reserved for the owners of seperate regiments and companies. As a rule these had to be bought and the cost of acquiring a regiment was so prohibitive that a petty nobleman had little chance of becoming a colonel.
For the nobility as a whole Louis had other means. Louis complied it to serve in the military, accustoming them to take orders as cadets in the gardes du corps (even though they worked as soldiers). There they were to learn to take orders and not to lift there head to much above the field. This policy was quite ruinous to the nobility because serving cost it much more money than it brought in, and so tended to incur debts. The king also took it badly if somebody wanted to quit his service, and had ways to insure that every noble boy entered the service.
In 1674 Louis took an extraordinary measure by invoking one of his feudal rights. Even though France was not in the situation where Louis had this right, he summoned every nobleman to take up arms and join him on horseback to serve for two months. Louis perhaps did this to show the nobility who was boss in France, and he could do it because the nobility received no compensation.
A useless class
The nobility had its place in society as long as it served its traditional role in the countryside and served in the military. Especially under Louis XIV this traditional role was hollowed out faster than ever before. In government by employing civilians in the administration and amassing the higher nobility at Versailles, and in the military by using armies so large that nobles were only a small minority. Maintaining a class that had no real function left other than to amuse the king and each other would soon become a nuisance to society. When the revolution came about in 1789 there was no strong provincial nobility that could save its monarch.