The Middle Ages saw the Christian Church peak in its political and social power. So great was their influence that the era is sometimes called the Age of Faith. However the same time period brought about great turmoil within the Church and its followers.
During the height of the Christian Church's influence in Europe the papacy had immense power over medieval society. As it is the Christians were devout followers at that time anyway. With the advent of the papal monarchy the pope wielded even more authority. This idea was that of pope Gregory VII. He created the papal court system whereby the papacy monarchy was run, though the pope had the ultimate say in all church affairs. The papal monarchy also had the right of excommunication with its followers. This was a major source of authority for the papacy.
The crusades were a major coming together point for the Christians. It was a way for them to unite and expand their religion. Imperialism being one of the major reasons for the Christian crusades. It was also said that they would go to heaven as a result of the crusades. Another reason for the crusades was to get Jerusalem under Christian rule. For the later crusades profit was also a reason. The first crusade began around 1095 and lasted about 4 years. There were several other crusades during the Middle Ages. Though the crusades were aimed at non-Christian regions, the 4th crusade changed that. During this crusade the city of Constantinople, which was already under Christian rule, was attacked and pillaged by French barons. Constantinople, also known as Byzantine, was robbed of its riches and Greek art and literature destroyed. This made the rift between East and West even greater.
The popes received large revenue sums from their extensive property holdings in Italy. On top of that they also received money from all over Europe from such taxes like Peter's pence and an annual tax on Christian families in England among other things.