Pope Gregory VII check the power of the Holy Roman emperor by: A. excommunicating him from the Church
At that time, both pope gregory VII and the holy roman emperor were involved in a conflict/disagreement regarding whether the emperor had the power to appoint church officials.
The emperor believe that the king should have the full control over the church while pope Gregory VII believe that there is a limit of what the kings can do, especially if the king want to intervene with people's faith
