In Medieval Armies sorry, left one word out of the title.
This is a thing I don't really understand. The Three Estates model is rather clear on the role of people: The First Estate, the church works on getting everyone else to Heaven, the Third Estate, the Peasents, work the land to feed the First Estate, ans the Second Estate, the nobles whose job it is to fight.
The entire Status quo was held up by this! Nobles got to be Lords and Masters of others because they supposedly fought for them, that was the reason (and convention, naturally) why people accepted their rule.
I always heard that gunpowder was important socially because it made it so that non-nobles now also fought in armies in large quantities, so they demanded more right on the basis of doing the job of te Second Estate.
But if peasents were soldiers, why did it take them hundreeds of years to question that model?
I really don't get this.
Your confusion is due to the fact that the Three Estates was an artificial and theoretical division of medieval society by medieval clergymen/scholars that glossed over actual conditions, and which was then repeated and expanded by earlier historians. Like feudalism, it is an inadequate model and a flawed lens through which to view the social history of the Middle Ages, ending in distorted results. I encourage you to forget the three orders for now.
Nobility is a created status, and one which emerged gradually and over time from the landed aristocracy. It wasn't like one day you had no nobility, and the next day these guys showed up claiming to be Those Who Fought. Rather, the landowning aristocracy that had been present since the early Middle Ages gradually developed the institutions and beliefs that we recognize as nobility. For more on this, see Crouch's Birth of Nobility. With that said, there was a widespread belief that the wealthy should take a leading role in military affairs, but we should keep in mind that they had reason to maintain men and arms: the protection of their property.
The reality is that social status was rather fluid and existed on a continuum. Even within the aristocracy, there were vast differences in status, from great territorial princes to landless knights or squires who earned their bread in service to another. Nor were the commons all one vast group. Medievals would not have viewed a small landowner or a burgher as being the same status as a poor serf, full stop. I'm really not usually a Marxist in my outlook, but I would suggest that a better way to view socio-economic status is to distinguish between those who controlled the means of production - land owners, burghers, etc - and those who depended on them to earn their bred.
It is true that France (and to a lesser extent England) demilitarized much of the commons over the course of the High Middle Ages. But lest you imagine some sort of sword-grabbing program, what I mean is a gradual shift in who was responsible for fighting. The levy of freemen of the Frankish kings gave way to a military system dominated by semi-professionals: lords and their military servants; urban militias; and mercenaries. This wasn't a sudden shift, but a gradual transformation of French society that took centuries.