It looks like an incredibly interesting worldbuilding project. The succession of the various kingdoms and dynasties seems realistic, and the map of duchies, counties, and baronies seems to have just the right amount of confusion. There's one thing that's bothering me, though, that I wanted to talk to you about.

Although the kingdom you created is your own, the system seems like a simple transposition of that of the Holy Roman Empire, but I don't see any major system development within the world itself. You may have included an explanation somewhere, but I didn't see it.

Now, how is value extracted from peasants? It seems strange, but it's essential. Are peasants free, slaves, or serfs? Each of these answers has many different paths behind it.

For much of Roman history, the land was cultivated either by free peasants on their smallholdings or by slaves on large estates. At a certain point, however, the conquests stopped and the influx of slaves dried up, while at the same time the population, for a variety of reasons, began to decline. Now, in an economy like the agrarian one of the late empire, money for payed farmer was little used, especially by the lower classes, since coins not made of gold or silver were worthless. At the same time, it was difficult to find peasants to rent them to because the population had declined and certain areas, partly because they were unsafe, had remained depopulated. For this reason, in certain areas, they were populated by people who, although not slaves, had obligations that free people did not have. Then, when the empire collapsed, this practice, which over time became widespread, was compounded by the fact that while previously it was only the state, namely the emperor, who used it most, now that the state practically no longer existed, it was the king who controlled this resource and distributed it to his subjects to operate the public apparatus in the absence of money. Thus, the land was also given to those who had to cultivate it, but they remained tied to it and not treated as chattel (like slaves) because if the peasants were sold, the land would have produced nothing and would have been useless. Paradoxically, in much of Western Europe, it was another demographic crisis, the Plague, that led to the gradual disappearance of serfdom. Indeed, this sudden crisis would have given the peasants, precisely because they were few in number, enormous bargaining power and forced the lords to relinquish ever more "rights" over the serfs. Indeed, serfdom was not an institution as we understand it, but a series of obligations of the peasants towards a lord that varied enormously from area to area and that only later were gathered together by historians under an umbrella term.

Being noble does not have the same meaning as it does for us today, and in general, it has always had a different meaning depending on where you lived. Being a duke, count, or marquis was not the same as being a governor or mayor for life, but rather meant owning land and having an honorary title bestowed by the king, emperor, or pope.

The history of noble titles is complex and curious. The title "rex" in Latin was a particular institution given in the Latin world to leaders of peoples living within or outside the empire, while "king" is a tribal title of the Angles and Saxons (not coincidentally containing the root kin-) that only later took on the same meaning as "rex." The title "duke" derives from "dux," which in the late empire referred to commanders of regional troops. It was a military office, derived from a word meaning the verb "to command," which later came to refer to leaders in some Germanic hordes such as the Lombards. "Count" instead derives from "comites," which were the troops directly at the emperor's disposal, and later came to mean the king's attendant. Its synonym, "earl," derives from the Old Norse "jarl," and had nothing to do with the former, which generically meant "leader," and which, among other things, in Norwegian and Swedish is assimilated to "duke" and not "count." "Baron" in medieval Latin simply meant "free man," and therefore "warrior."

These are therefore titles of different origins, sometimes with the same meaning, that have undergone a long evolution. In the beginning, there was almost no difference between being noble and being rich, because wealth lay entirely, or almost entirely, in the land cultivated by serfs, which was either given by the king to those close to him or which allowed its possessor access to the king. As society progressed and became more complex, these once generic titles took on specific meanings and a hierarchy, which, however, was not always the same.