Federalism prevented any single state from resolving the divorce-law contradiction.

Evidence

Divorce law was an egregious example of a branch of law tortured by contradictions in public opinion, trapped between contending forces of perhaps roughly equal strength; trapped, too, in a federal system with freedom of movement back and forth, and beyond the power and grasp of any single state. The dual system lasted deep into the twentieth century. — Lawrence M. Friedman, A History of American Law, 2898

Categorization

• XREF: Federalism’s structural role in producing the dual system is the same tension but no single state held enough power to fix it — echoes the reader’s thread on free interstate mobility turning states into competing law-sellers.