Conquest and law are necessarily intertwined subjects. Conquerors seize not only a territory, but also sovereignty over a people. Usually the most visible display of this sovereignty is a conqueror's issuance of laws to better control or reshape what they have conquered. The Roman empire, the model state for many early medieval kingdoms, expanded its sovereignty over many independent peoples through military conquest, and followed up these conquests by imposing its law. The most famous of early medieval conquerors, Charlemagne, with his eyes on Rome, amended and fixed in form the laws of the peoples he had conquered or subordinated. In the most extreme case, he reinforced his brutal military conquest of the Saxons by issuing harsh laws to suppress their pagan religion and eliminate their political independence. Conquest was one of the preferred times for a new sovereign to impose new laws or to authorize old or existing ones. Both imposition of the new and authorization of the old were options and were often done at the same time, in the same piece of legislation.

We often treat the laws issued after a conquest as a litmus test for the level of change or continuity experienced by the conquered people, which is not unwarranted, given that laws are reflections of the policies arising out of political agendas. This, of course, is a very top down view of what a text purporting to describe the law actually represents. It also presumes the authenticity of records of the law. For the most part, texts of law codes are treated by historians as if authored by the kings whose names appear in their prologues. That the laws were the historical law-giver's is no doubt often the case. Not many historians would doubt that Roman imperial rescripts reflect the decisions of the imperial court of this or that emperor. In the same way, the laws aimed at the Saxons are considered by historians to be genuine reflections of the attitude and strategies of the Frankish conquerors who issued them.

Of course, things are not always as simple as they first appear. Early medieval law has a more complicated relationship to conquerors and to the conquered than can be explained by claiming that law reflects a winner's decision to change or maintain the existing laws of a conquered state.