The Decline of the Church
The biggest cause of the Church's downfall was its claim to papal authority. Their claims began to become more and more over the top and they seemed to claim an increasing amount of authority over other kings and Emperors. This as one could imagine didn't go over well and the Church met its decline soon after its peak in the 1200's.
Boniface VIII and the Conflict with the State
A pope from 1294 to 1303 Boniface VIII is deemed the pope in power when the church and state fell into conflict. Boniface's real problem came in the form of the French King Philip IV (1285-1314). The big problem was, as mentioned above, the struggle for ultimate authority between the church and its claim to papal authority and the secular kings. Specifically in the instance between Boniface and Philip, the French King wanted to claim a larger income and in turn decided, for some odd reason, to tax the clergy. This didn't sit well with Boniface as he believed that this couldn't take place without his divine assent, whereas Philip believed that all French people, including the clergy, were under his authority as king.
In an attempt to assert the Church to a higher position than Philip and the French Boniface quickly excommunicated Philip in a letter known as the Unam Sanctam in 1302. This obviously angered Philip and soon after his excommunication he took Boniface by force and had intentions to try the pope in a French court of law if, that is, the Italian nobles and country men hadn't rescued him first. Boniface died soon after being kidnapped and through his death the secular monarchies had won a significant victory over the church. Because of these events no pope has ever laid claim to so much as Boniface has ever again.
Afterwards Philip took measures to ensure nothing would come so close to removing him from the French throne again and convinced the Church to elect a French pope.
In an attempt to assert the Church to a higher position than Philip and the French Boniface quickly excommunicated Philip in a letter known as the Unam Sanctam in 1302. This obviously angered Philip and soon after his excommunication he took Boniface by force and had intentions to try the pope in a French court of law if, that is, the Italian nobles and country men hadn't rescued him first. Boniface died soon after being kidnapped and through his death the secular monarchies had won a significant victory over the church. Because of these events no pope has ever laid claim to so much as Boniface has ever again.
Afterwards Philip took measures to ensure nothing would come so close to removing him from the French throne again and convinced the Church to elect a French pope.