I declare that I can choose bishops and remove emperors.
Yes I can!
Then I'm not following them!
You can't do that!
Once there lived a king in Europe named Charlemagne. His goal was to establish a Christian Empire. Later, Pope Leo III asked for Charlemagne's protection from being removed from office. Charlemagne agreed and was crowned Holy Emperor because he helped the Pope. This made the Byzantine Emperor mad because now Popes can crown Emperors.
How dare you not follow my rules! Now you must pay for your actions... I'm excommunicating you!
Charlemagne believed that God had made him Emperor in order to do God's work on Earth. However, Pope Leo believed that the church made Charlemagne emperor. Two hundred years later, the different views led to a dramatic clash between an Emperor and Pope.
Please forgive me, Pope Gregory
Fine. I'll forgive you this one time. But, this will not happen again.
Two hundred years later in 1073, a new Pope named Pope Gregory made a set of rules declaring his supreme authority over both Church and secular leaders. He gave himself the privilege to add bishops and remove emperors. King Henry IV was angry with Pope Gregory's new rules, so he decided to not follow Pope Gregory's rules.
The church can now choose bishops. Also, it lets emperors give grants of land to win the loyalty of bishops.
We have established the Concordat Of Worms!
King Henry didn't like Pope Gregory's new rules, so he decided to not follow them by naming his own Bishop. This angered the Pope so he appointed a rival bishop. Then, Henry decided to try and remove Gregory as Pope. Gregory removed Henry from the church and freed Henry's subjects from their feudal oaths.
King Henry wanted Pope Gregory to forgive him, so King Henry stood in the snow outside of the Pope's castle for three days. Finally Pope Gregory forgave him. Later, Henry wanted revenge on the Pope, so he took his army to Rome and forced the Pope from office.
Finally a resolution was made to solve the conflict between Popes and Kings. This resolution was called,The Concordat of Worms. It gave the Church the right to choose bishops. However, it was unsuccessful because later Pope's and Kings still had conflicts with each other.