Noble Lords have the power to arbitrarily make laws and impose various taxes. In simple terms, once a Noble Lord paid the kingdom's specified taxes, they could do whatever they wanted with their territory.
Theoretically, a lord could impulsively slaughter all their subjects within their territory. Of course, this would only occur if a lord was a follower of a demon or a devil or was mentally deficient. Even if the royal family ignored such an act, there would be many righteous individuals who would intervene.
Normally, Noble Lords would not murder indiscriminately, yet the commoners' living conditions were generally not much better because Nobles wouldn't treat their subjects as equals.
In fact, most nobles treated their subjects as livestock. The Nobility, naturally commanding extraordinary powers, and the powerless commoners were essentially two different species.