The Deathworld Trilogy

The planet was unknown¿ a savagely primitive place where every man had to kill every other man - or live as a slave. The inhabitants lived in the early Bronze Age one minute, and in the early Machine Age the next. Technology had degenerated into a number of mysteries jealously guarded by separate brotherhoods. But Jason dinAlt was a gambler. He realised that if he was ever going to get a winning hand in this game, the brotherhoods would need a shuffle¿