A kingdom where, if there are multiple princes (princesses can't rule unless they have no siblings), the princes fight to the death in the arena to decide who gets to rule. A simple way to make sure your brother cannot make a bid for the thrown, and keeps the royal blood in one line.
What if the sources of precious metal in the realm all failed, so that the only sources for gold and other precious metal were hostile foreign lands? Gold coinage might become increasingly rare, resulting in hoarding. Player characters that appear with masses of treasure might be suspected of being in the pay of foreign powers.