"It takes an awful lot of people, working together at an awful lot of jobs, to keep a civilization running. Smash the installations and kill the top technicians and scientists, and the masses don't know how to rebuild and go back to stone hatchets. Kill off enough of the masses and even if the planet and the know-how is left, there's nobody to do the work. I've seen planets that decivilized both ways." from The Space Viking, by H. Beam Piper
In Spy by Ted Bell, The Xucuru warriors of the Amazon are about to wipe out a boat crew. The boat has all sorts of high-tech weaponry, but has to travel very slowly. The Xucuru are primitive, almost naked, using blowguns and poisoned arrows. How to stop them from boarding the vessel? Carpet tacks spread all over the deck.