Neobarbarians

"These are homemade barbarians. Workers and peasants who revolted to seize and divide the wealth and then found they'd smashed the means of production and killed off all the technical brains. Survivors on planets hit during the Interstellar Wars . . . who lost the machinery of civilization. Followers of political leaders on local-dictatorship planets. Companies of mercenaries thrown out of employment and living by pillage. Religious fanatics following self-anointed prophets."

Space Viking, p. 12, by H. Beam Piper