How did popes in the 11th century use excommunication and interdict as political tools?

Excommunication, the formal process of banishing someone from the Church, and interdict, a formal measure which bans certain Church members from participating in specific holy rites, were used extensively by the 11th century popes. Since the Church was the dominant social institution, its power was interwoven with that of other political structures, and popes were able to use these tools to apply coercion or removal to those who disagreed with them. For example, the Holy Roman Emperor Henry IV was excommunicated on four separate occasions due to his disagreements with Gregory VII and Urban II.