Some historical context
Romans used to subject their lands to the province system, but with the massive migrations big swathes of lands became settled WHILE UNDER THE ROMAN ADMINISTRATION by germanics, so romans updated the foederati system https://es.wikipedia.org/wiki/Foederati
Which used to be synonym of a superior / inferior system between two polities, roman being the superior, into a real federal system that gave germans de facto control of former provinces as a form of payment, in a context of progressive depopulation.
So, the leaders of these lands had a pact, a treaty, a vincular relationship, between them and the roman central government, this relationship then was in turn used between these germanic leaders and their own subject, in a form of a military administrative delegation of faculties.
With time these de facto ownership became institutionalized as what we know as feudalism, depopulation and the need to control of big swathes of land, gave room to the birth of localised systems minimally related to a central figure mimicking the relationship between the old germanic tribe leaders and the roman central government. They turned these relationships private in nature, and land became property of these warlords, which in turn -according to civil law- was given to the children, generally partitioned until that was no longer feasible either by geopolitical needs or technological progress / stability.
So imagine it goes like this
Less to more federal
US > CSA > HRE > Low middle Ages