The nobility declined because of their destabilizing effect on society - the kings could not trust them to be loyal in matters of allegiance and religion.
In England, the Wars of the Roses made the nobility a perpetual danger that the monarch wanted to crush.
In France, the Wars of Religion created the same lack of trust.
The Holy Roman Empire collapsed as an effective political unit because of the nobility refusing to agree on any Empire-level initiatives.
All this was a function of the nobility becoming to wealthy, to well armed and too dangerous for the monarchs to tolerate.
That POV never got on really big in Europe
I agree, but it did get on big in the UK.
The reason for this, in my opinion, is the inflexibility of European social structure due to: (1) primogeniture, (2) endogamy among elites and (3) the Salic law.
In the UK a successful peasant's son could go into trade or buy a commission in a regiment and quickly gain social status. His son could wind up becoming a knight or other minor nobility or potentially getting a high-ranking civil position. Along the way, he could marry a poor but titled woman and move up socially as well.
In prerevolutionary France, as Furet has pointed out, it took four generations just to become an officer or low ranking civil servant. There was close to zero social mobility - the rise of a family was measured in centuries, not decades.
In America, the process was even quicker than in the UK.
I guess we’re going to have to disagree on the military history front.
The various wars you describe are all, IMO, examples of wars that at root were desperate attempts by the nobility to maintain their crumbling position in society.
The power that wealth gives a person or group in society could be mathematically expressed as a percentage of the total wealth.
During the Middle Ages, the nobility, with the King generally considered primarily the first in rank of the nobles, controlled the vast majority of every country’s wealth. The upper ranks of the clergy were also very wealthy, but they were in reality mainly a branch of the nobility, being usually younger sons of aristocrats.
With the early modern period, the King, generally with the enthusiastic support of the commoners, isolated himself from and put himself far above the nobles. High nobles fought over the privilege of carrying away the Sun-King’s chamber pot, whereas their ancestors would have cut the King’s throat for suggesting such a thing.
The nobility’s share of wealth declined precipitously throughout the early modern period, while the King’s went up, and that of the commoners went up even faster. This decline of the nobles was on the Continent exacerbated by the practice of considering all sons of nobles to be noble. In England, only the heir was noble, his brothers and sisters were commoners.
That is why the nobility in France in the second half of the 18th century competed so desperately for positions at court. It was generally the only way they could maintain their illusion of wealth and power. They expanded the need for patents of nobility even further for positions, because in many cases their nobility was all they had, and they were trying to increase its value.
BTW, the middle ages and early modern eras, even on the Continent, had a good deal more social mobility than commonly thought. What you describe was the theory. The reality was a lot more flexible. A commoner who became wealthy could take advantage of a thriving trade in phony patents of nobility. Families often went up (and down) a lot faster than theory would allow.
I think I may have been incomplete in my explanation of why the aristocracy lost military relevance.
Their power and position in society in the Middle Ages was based on their master of very specific military skills, those of an ultra-heavy cavalryman or knight. In fact, in I believe all European languages other than English, our word “knight” is translated with a word that also means “rider.”
The nobleman was a warrior who rode to battle in armor. The skills necessary to fight effectively this way took many years to acquire and constant practice to maintain.
It utterly lost any military relevance when armies of commoners developed effective ways of fighting them.
The Swiss and their pike squares and the English with their longbows dented but did not destroy the place of the armored knight. These weapons systems still took a great deal of training, and in the case of the Swiss pikes extreme esprit de corps and morale.
But as gunpowder weapons became more and more effective, any peasant could be trained in a matter of weeks (at most) to be more effective on the battlefield than a knight who had spent decades learning his skills.
Except as commanders, the nobility promptly became irrelevant as warriors. No function, and people started to wonder why they were supposed to honor them. Which was a very good question.