What Was the Most Important Factor That Limited the Effectiveness

What was the most important factor that limited the effectiveness of all medieval European monarchies?

A) The hereditary succession system often led to dynastic interruptions and disputes.
B) Secular rulers had to accept the right of the pope to appoint kings.
C) Continued barbarian raids forced kings to focus on defense rather than improving their own country.
D) The European economy was too weak to support more effective states.
E) Poor nutrition and hygiene meant that devastating plagues were common,even among royals.