What are sacraments, and how did an interdict affect them? why was a pope’s use of an interdict such an effective method of controlling rulers?

Sacraments were little tokens that you got to "forgive your sins"

It made the Church the greatest influence on the government

Hope this helps! 

    The sacraments are effective signs of grace, instituted by Christ and entrusted to the Church, through which the divine life is dispensed to us.      The visible rites under which the sacraments are celebrated signify and perform the graces proper to each sacrament. They bear fruit in those who receive them with the required dispositions. The Holy Spirit prepares for the reception of the sacraments through the Word of God and the faith of those who receive in their hearts. The fruit of sacramental life is both personal and ecclesial. On the one hand, this fruit is for every believer a life for God in Christ Jesus; on the other, it is the growth for the Church in charity and in its mission of witness.

    The sacraments of the new law were instituted by Christ and are seven: Baptism, Confirmation, Eucharist, Penance, Anointing of the Sick, Order and Marriage. The seven sacraments reach every stage and every important moment of the Christian life: they give the life of faith of Christians origin and growth, healing and mission. In this there is a certain resemblance between the stages of natural life and those of spiritual life.

    In Catholic canon law, an Interdict is an ecclesiastical censure, more specifically a prohibition that hits certain people or groups of the Church becoming unable to participate in certain rites, may also mean that the rites (sacraments, masses, etc.).

the answer to your question is:

strong-mayor system