Gonzalez, Justo L. The Story of Christianity: The Early Church to the Reformation. Revised and Updated ed. Vol. 1. New York: HarperCollins, 2010. Kindle Electronic Edition.
Ch. 31, “The Offensive Against Islam” Loc. 6026-6221.
The Crusades were waged out of a desire to take back areas which had been overcome by Islam through military force. Though the Crusades did briefly liberate Constantinople and bring a brief period of a united East and West in the Church, the results were temporary (Gonzalez 2010, Loc. 6034).
The first crusade, launched in 1095 but Urban II, sought to take back the Holy Land from the Turks (Gonzalez 2010, Loc. 6056). The forces were not well governed and tended to engage in conflicts as they moved through allegedly friendly territory. After taking Nicea, then Antioch with great difficulty, they moved by June 1099 to Jerusalem (Gonzalez 2010, Loc. 6084). The city fell in chaos on July 15, 1099 (Gonzalez 2010, Loc. 6094). While many of the Crusaders then left, there were frequent small armed forces coming from Europe to provide support (Gonzalez 2010, Loc. 6105). These movements had less centralized organization.
A second crusade came after the fall of Edessa in 1144. Nearly 200,000 troops were repeatedly defeated before disbanding (Gonzalez 2010, Loc. 6116). A third was launched after the fall of Jerusalem in 1187. This one too accomplished little (Gonzalez 2010, Loc. 6127). A fourth crusade resulted in a new Latin emperor in Constantinople, followed by disputes between East and West in the Church (Gonzalez 2010, Loc. 6137). A fifth then sixth crusade sought and eventually captured Jerusalem, then by 1270 a seventh crusade resulted in the imprisonment and death of Louis IX of France (Gonzalez 2010, Loc. 6147).
In connection with the various Crusades Gonzalez discusses the Spanish Reconquista, an attempt to take Spain back from the Muslim invasions of the 8th century (Gonzalez 2010, Loc. 6147). By this time in many areas there were family alliances between Christians and Muslims. Due to various revolts the Caliphate was losing power in Spain in the 11th century (Gonzalez 2010, Loc. 6168). Christian forces took back the territory, mostly during the 13th century (Gonzalez 2010, Loc. 6168).
Much of the outcome of the Crusades was embodied in mistrust between Islam and Christianity as well as between East and West (Gonzalez 2010, Loc. 6179). There also developed a greater emphasis on relics, monastic and military orders, and pilgrimages (Gonzalez 2010, Loc. 6188). The Church tended to be more free in endorsing military action. Also a greater interest in philosophy and theology from foreign lands developed (Gonzalez 2010, Loc. 6198).