Being brought up believing you have a divine right to rule and a duty to enlarge your kingdom isn't a selection effect, but worked to pretty much the same outcome in terms of brutality. Even in European states where there were pretty straightforward primogeniture rules of succession, you ended up with hundreds of years of "legitimate" inheritors displaying fondness for foreign military expeditions and tactical ploys to acquire tendentious claims to other territory, and as soon as a direct adult male descendant from a single wife wasn't available succession selected for ambition and ruthlessness considerably more than a parliamentary system.