Why did feudal lords apply the same local law to tenants of different origins?

Feudal lords applied the same local law to all tenants, regardless of their racial or national origin, to transition away from the traditional Germanic "personal principle" of law. Under the earlier Germanic system, individuals were often judged according to the laws of their specific tribe or ethnic group.

As feudalism emerged and government became highly decentralized following the disintegration of the Frankish kingdom, lords gained significant power over their territories. By applying the custom of the region—or the "territorial principle"—to all inhabitants within their jurisdiction, lords established a more uniform legal framework that was easier to manage and better suited to the new social and economic conditions of their estates. This feudal law was typically a blend of Germanic customs and Roman law, adapted specifically to serve the interests and authority of the feudal lords.1