Legal systems define an abstract interface between individuals in a society. It's interesting how Japan's registration system choose different entities and different 'ACL rules' compared to, say, US common law.

Seems like it'd be tricky to build a koseki-like registration here. Legal abstractions have a lot of inertia, and usually requires some sort of war or revolution to precipitate change.

For example, most of Western Europe's legal systems are based on the Napoleonic code, spread by conquest, and was largely written after the French Revolution to sweep away the last vestiges of the monarchy and feudalism. Japan's modern koseki system was created right after the Meiji Restoration.