Harry Harrison 
Deathworld Two 
Deathworld Book 2

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 din Alt 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