The Supreme Court, of the federal united States, decides Swift v. Tyson: federal courts that must decide a controversy not specifically addressed by a State legislature have the authority to develop federal common law.
[added 9/7/2026]
Subsequent Events:
Authority:
Article VII of Amendment
ccc-2point0.com/constitution-for-the-united-states
References:
Swift v. Tyson – Wikipedia
en.wikipedia.org/wiki/Swift_v._Tyson