Before the Millennium, the papacy sought to break free from the rule of the emperors of the Holy Roman Empire. This struggle for investiture ended in the victory of the Church. The ambitious and ambitious Pope Gregory VII started the largest-scale ecclesial reorganization reform, named after him Gregorian. On the one hand, this pontiff tried to muffle popular criticism of the clergy and restore the shaken authority of the clergy by introducing celibacy and creating new monastic orders with a strict charter. On the other hand, the pope tried to curb the ever-expanding class of landless (due to the right of the majorate) knights. The younger sons of the feudal lords, being rightfully born people of the sword, represented a "time bomb" for society. The announced "Days of the Peace of God" - prohibitions to conduct hostilities on certain days - did little to save the situation. These factors - the desire to strengthen the reverence for the clergy and the huge mass of restless armed people - and prepared the first crusade.
After the mutual curses that the Pope and the Patriarch of Constantinople exchanged in 1053, the two Churches finally parted. However, when the Seljuks invaded the Byzantine Empire, Vasilevs Alexei I Komnin asked the Western European sovereigns for military assistance. Such a plight of Byzantium was very much in the hands of the papacy. It was possible not only to send a huge mass of chivalry overseas, but also to strengthen the authority of the Church by leading the first crusade. But for this it was necessary to turn the usual secular conflict over lands into a holy war for the Holy Sepulcher. However, in order to become the head of this military campaign, pushing the excommunicated Henry IV of Germany and Philip I of France, it was necessary to make one important theological twist.
Until that time, the Church called killing sin and war a sinful thing, or at least a lesser evil. Now she was faced with the task of calling “black white” and directly getting involved in bloodshed. Using the image from the Revelation of John about the struggle of the archangel and the angelic army with the army of the Antichrist, the Roman papacy spoke of righteous wars. So in the fall of 1095 in Clermont (now Clermont-Ferrand in France) at the church cathedral, Pope Urban II announced the sacralized first crusade. And then theologians substantiated this with statements that killing a wrong person, no murder is committed, but on the contrary, the eradication of evil takes place.
On the way to the Holy Land, the crusading army was distinguished by large-scale Jewish pogroms, and the capture of Jerusalem in 1099 led to such a massacre that, according to the memoirs of Fulko Chartres, "the legs sank into the blood of murdered wives and children ankle-deep." And over all this the cry of the “Christian” army thundered: “This is pleasing to God!” This campaign turned over the medieval foundations of society. The path began to slide towards an almost totalitarian “society of persecution”, as R. Moore aptly puts it, when certain groups of the population were expelled from society (declared enemies of God): Jews, religious dissidents, Orthodox, lepers, etc. It is difficult to say exactly how many crusades there were, because not all of them were officially declared by the papacy (there were 8 of them), but only inspired by sermons.
One thing is certain: from the time of the first invasion of the Holy Land, the killing of someone whom the Roman Catholic Church points to as an enemy was no longer considered a sin, but the highest religious virtue. In the XIII century, when the first crusade was proclaimed in Christian lands (against the Albigensians), tolerance was declared a sin. At the IV Lateran Council in 1215, Pope Innocent III declared the enemies of the Lord schismatics, that is, Orthodox Christians. And already in 1232, Gregory IX called on the good Catholics to sew the cross and go to fight against Novgorod and Pskov. The military campaign continued with varying success from 1232 to 1240, until the Battle of Lake Peipsi in April 1242 (called the Battle of the Ice) put an end to the claims of the Roman papacy to the Eastern Slavic lands. It is difficult to imagine the fate of the Slavic peoples if the crusades in Russia would end differently, because in his bull (12/12/237), Gregory IX calls on the crusaders to ruthlessly “destroy the enemies of the cross”.