In SM Stirling's Conquistador (New York, 2004), the Commonwealth of New Virginia is kind of retro-feudal in that its territory is divided into domains belonging to economically and politically powerful lineages, the "Thirty Families," and there is a patron-client relationship between Family "Primes" and their employees. However:
there are no serfs bound to the land;
there is church-state separation;
there is multi-denominationalism;
there is a defense force for the Commonwealth as a whole, not for each domain as against others;
they have modern technology and can build their own aircraft.
The Families include:
"'...the Sanderses, farther up the river...'" (p. 429)