Final answer:
Pope Innocent III used the interdict to control the rulers of Europe by suspending religious services in their lands, impacting all subjects and pressuring rulers to comply with his wishes.
Step-by-step explanation:
Pope Innocent III used various means to exert his influence over the rulers of Europe, but one of the most effective penalties he employed was the interdict. An interdict was a church order that suspended the performance of religious services in a ruler's lands. This form of ecclesiastical censure was broader than excommunication, which affected only an individual, and it proved to be an effective tool in bringing rulers to obey the Pope's desires as it deprived the people of a ruler's realm from the church's sacraments, which was a severe punishment in a deeply religious era.