The sentence discusses the relationship between rulers and subjects. The phrase "corrupted by too much power" fits well for the rulers, and "corrupted by too much passive obedience" fits the subjects, as it suggests that they lack active participation and are subdued by the excessive control of the rulers.
Option (A), formed by a small minority ... who are uncivilized, is incorrect because it makes an unfair characterization of the subjects, implying they are uncivilized, which is irrelevant to the idea of power imbalance.
Option (B), powerfully corrupt ... pointless crusaders, introduces terms that don’t match the context of the power dynamic between rulers and subjects, and "crusaders" doesn’t fit.
Option (D), who are ruled ... who ruled, is a weak choice because it repeats the same idea without adding any depth or explaining the nature of the relationship between rulers and subjects.
Thus, option (C) is the best choice.