In the Middle Ages, popes and kings started ruling after Rome fell. But, they always argued about their power.
Kings didn't like how popes had the real power, since they controlled the church and spiritual part.
The most effective known argument was between King Henry and Pope Gregory.
I, the new Pope, do not agree with the new bishop you have chosen, Emperor Henry IV.
How dare you! Germany bishops, I command you now to kick out the pope, Gregory VII!!!
Fine then, as a response...YOU SHALL BE EXCOMMUNICATED!
Emperor Henry was excommunicated, and begged for forgiveness to return back to royalty to Pope Gregory.
This was supposed to be an example to others. In the end, after future discussions, kings and popes came to the new rules. Popes would choose the bishops and abbots, but would still have to obey the emperor.