Hello. I'm writing a fantasy history, in a complete fictional world. I want to establish a narrative that makes a group of humans previously organized in tribes, to change their administration and secular structure of power into a Feudal monarchy.
First I thought on some historical examples on how it came to be, and so the real life parallels I could think of were the Goths, the Lombards and the Frankish. Still, they don't really fit with what I am aiming for. I've been wandering how did more distant realms been formed as Duchies and Kingdoms, those of the Baltic States, for instance, that I imagine were less susceptible to Roman influence than the Goths or the Frankish. It seems that roman catholicism played a major part on it, but to what extent? How did those people assimilated catholicism in their culture or how did they resist? What reasons did they had to accept a King instead of a tribal leader?
The development of feudalism is the result of localized authority in a primarily agrarian economy. With the collapse of the imperial systems and institutions power and authority devolved from the offices of the empire to the local magnates and estate holders that owned the land.
Significant consequence was a greatly diminished trade, particularly long distance, and sharp reduction in the availability of money. This means that trade became local and barter focused.
The upshot of this is that, since everyone needs to eat and food comes from the soil, if you owned land you were in a position to negotiate for labor - thus serfs, primarily defined by their connection to the land, but who had various levels of freedom.
The Serf offered their labor (on the land, but in military service such as it might be) to the land lord. The landlord in turn protected and provided for the Serf. As trade recovers, and money becomes available, serfs are able to improve their lot through their greater economic power.
If you have enough land you might partition some of it and entrust it to another person, who would manage it for you and provide you with proceeds from the harvest and other (mostly agrarian) economic activity from it.
These land owners become the locus for administration and legal activities since they are the closest thing to authority in this mileau.
Eventually some of the farming villages become centers of trade, and wealthy non landowners have the means to apply pressure previously only available to the landed magnates. You see the development of guilds and representative assemblies and the decline of the manorial system.
When money can be accumulated, the old feudal system starts to shift as now the rich and powerful pay for labor and military service with money instead of relying on the feudal relationship.