Complex sentence: A war between the citizens and their bishop was paid dearly when in 1519 to 1523 they engaged in a feud, and soon the town became protestant, and only the cathedral and a few more buildings remained in imperial (catholic) hands.
Split into simpler sentences: A war between the citizens and their bishop cost dearly in 1519-1523 when they engaged in a feud. Soon the town became protestant, and only the cathedral and a few other buildings remained in imperial (catholic) hands.