History of Christianity
Pope Gregory VII issued the Dictatus Papae, which said only the pope may make, break, or move bishops to other sees.  The Emperor rejected this.  With excommunication and a revolt by his dukes, Henry apologized and was forgiven, though the conflict continued.  A similar controversy happened in England between King Henry I and St. Anselm, Archbishop of Canterbury.  The English dispute was resolved by a deal in 1107, where the king gave up making bishops but did require an oath of fealty.  The later Concordat of Worms (Pactum Calixtinum) resolved the Imperial investiture controversy with a similar compromise.