In the 7th century the prophet Muhammed founded Islam, which means “submission.” Islam is a monotheistic, Abrahamic faith that preaches the goodness, mercy, and power of God; the transcendence and distance of God; a coming Day of Judgment; and charity (the zakat of the Five Pillars of the faith). Through various conquests Islam spread through Africa, the Arabian Peninsula, and the Middle East, but did not break into the Western Roman Empire because of the defense of Charles Martel’s army at the Battle of Tours in 732. That no empire stood in their way and that the Qu’ran instructed this preaching and conquest contributed to the Muslim success in extending religious influence.
Though Western Europe was spared Muslim conquest, Eastern Europe, where Constantine had established his seat of government, was not. By 1095 a Sunni Muslim people, the Seljuk Empire, had overtaken much of the Byzantine Empire. Emperor Alexius petitioned Pope Urban II of the Western Roman Empire for help in repulsing the Turks. The ambitious Urban II seized the opportunity to enhance his power and super-glue the Catholic Church to the sociopolitical map.
The plan was to defend Constantinople, but Urban II and Western European society had several other aims in pursuing what would be the First Crusade. A key one was reclamation of the Holy Land, which Urban II, in his sermon at the Council of Clermont in November of 1095, claimed the Turks had “depopulated” of honest Christians by “the sword, pillage and fire” and unrightfully invaded. He called Christians to join in the cause to liberate the royal city from that heathen hands who were “utterly alienated from God.” (The quotations from this sermon are from Original Sources of European History, vol. 1, printed by the University of Pennsylvania in 1910.)
For the pope, the Crusades brought political power. For the layman, the Crusades offered the opportunity for purification of his soul – spiritual redemption, an especial concern for the common man of the 11th century who feared the contamination of sin. The pope promised the soldiers who embarked on the quests indulgences, which might be called Purgatory versions of Monopoly’s get-out-of-jail free card. (Purgatory, in Catholic doctrine, is an interim period between death and Heaven, where Christians who died with sins left to expiate may fully purify themselves.)
After aiding the Byzantine Empire in 1095, the Roman Catholic Church sanctioned seven other major Crusades through the 13th century with the aim to gain permanent control of the Holy Land from the Muslims. The Crusaders did not accomplish this goal, and in this period engaged in much back and forth with their enemies over Jerusalem.
Notwithstanding this failure, the Crusades were not thereby useless. In fact, the Crusades played an important role in ushering in the Renaissance. The conquests exposed Europeans to the Eastern ideas about mathematics, philosophy, and medicine and, as merchants discovered the merchandise to be had and sold, stimulated trade and economy. Wealth increased and cultural interests were piqued. The Crusades, while filling the Holy Land with blood, breathed new air into European society.