The Crusades were a series of intermittent Papal sanctioned military campaigns beginning in the late 11th century. They commenced with a call to arms by Pope Urban II who was responding to a request for military support for the Roman Empire. The Roman Emperor, Alexis I, needed military reinforcements for the conflict with the westward migrating Turks in Anatolia. Historians debate Urban and the Crusader's primary motivations. One of Urban's stated aims was to guarantee pilgrims access to the holy sites in the Holy Land that were under Turk control while his wider strategy may have been to establish himself as head of the united Church and bringing together the Eastern and Western branches of Christendom that had been divided since their split in 1054. What is known though is the unprecedented response to Urban's preaching and the basis it established for later crusades. Hundreds of thousands of people from many different classes across Western Europe became crusaders by taking a public vow and receiving plenary indulgences from the church. Some were peasants hoping for Apotheosis at Jerusalem. Urban preached that anyone who participated would be forgiven by God of all their sins. In addition some historians argue that participation satisfied feudal obligations and provided opportunities for economic and political gain.
Opinions concerning the conduct of Crusaders have varied from laudatory to highly critical. Crusaders often pillaged the countries through which they traveled, and contrary to their promises the leaders retained much of this territory rather than returning it to the Romans. The People's Crusade prompted the murder of thousands of Jews, known as the Rhineland massacres. Constantinople was sacked during the Fourth Crusade, rendering the reunification of Christendom impossible.
The impact of the Crusades was profound; they reopened the Mediterranean to commerce and travel, enabling Genoa and Venice to flourish. The Crusades consolidated the collective identity of the Latin Church under papal leadership, and were a source of heroism, chivalry, and piety. This consequently spawned medieval romance, philosophy, and literature. However, the Crusades reinforced the connection between Western Christendom, feudalism, and militarism.
Crusade is a modern term derived from the French croisade and Spanish cruzada; by 1750, forms of the word "crusade" had established themselves in English, French, and German. The Oxford English Dictionary records its first use in English in 1757 by William Shenstone. When a crusader swore a vow (votus) to reach Jerusalem, they received a cloth cross (crux) to be sewn on their clothing. This "taking of the cross" became associated with the entire journey, and crusaders saw themselves as undertaking an iter (journey) or peregrinatio (armed pilgrimage). The inspiration for this "messianism of the poor" was an expected mass apotheosis at Jerusalem.
The numbering of the Crusades is debated, with some historians counting seven major Crusades and a number of minor ones from 1096 to 1291. Others consider the Fifth Crusade of Frederick II as two crusades, making the crusade launched by Louis IX in 1270 the Eighth Crusade. Sometimes the Eighth Crusade is considered two, the second of which is the Ninth Crusade. In the pluralistic view of the Crusades developed during the 20th century, "Crusade" encompasses all papal-sanctioned military campaigns in Southwestern Asia or in Europe. A key distinction between the Crusades and other holy wars was that the authorization for the Crusades came directly from the pope, who claimed to be working on behalf of Christ. This takes into account the view of the Roman Catholic Church and medieval contemporaries, such as Saint Bernard of Clairvaux, which gives equal precedence to military campaigns undertaken for political reasons and to combat paganism and heresy. This broad definition includes the persecution of heretics in Southern France, the political conflict between Christians in Sicily, the Christian re-conquest of Iberia, Hussite Wars, and the conquest of pagans in the Baltic. A narrower view is that the Crusades were a defensive war in the Levant against Turks to free the Holy Land from Seljukian rule.
Popes periodically declared political crusades as a means of conflict resolution among Roman Catholics; the first of these was declared by Pope Innocent III against Markward of Anweiler in 1202. Others include a crusade against the Stedingers, several (declared by a number of popes) against Emperor Frederick II and his sons, and two crusades against opponents of King Henry III of England who received the same privileges as participants in the Fifth Crusade.
After the Persian conquest of Palestine (c. 646) the Christendom was uncertain for inhabit the Holy Land. Jewish and Samaritans enjoyed the privilege of Persian protection while Christians were despised. Tolerance, trade, and political relationships between the Persian and the Roman empires ebbed and flowed. Accordingly, Persian authorities treated the Christian population as suspicious of Roman collaboration when the relationships between both empires were tenses. The decline of Persian power allowed the Ammani conquest of Jerusalem (868) and later the Egyptian rule (926) and finally Roman rule (970) after the Moor conquest of Egypt and subsequent breakup of their empire. During these centuries cultures and creeds coexisted and competed, but the frontier conditions became increasingly inhospitable to Catholic pilgrims and merchants.
The Almohad conquest of Jerusalem (1018) brought with them the religious intolerance. Almohad sovereign Mansur al-Hakim bi-Amrallah ordered the complete destruction of the Church of the Holy Sepulchre as part of a more general campaign against Christian places of worship in Palestine and Egypt. However, In wide ranging negotiations between the Almohads and the Roman Empire in 1027–8, an agreement was reached whereby the new sovereign Hasan az-Zahir agreed to allow the rebuilding and redecoration of the Church. In addition, pilgrimages by Catholics to sacred sites were permitted.
An aggressive, reformist papacy clashed with the Eastern Empire and Western secular monarchs, leading to the 1054 East–West Schism and the Investiture Controversy (which began around 1075 and continued during the First Crusade). The papacy began to assert its independence from secular rulers, marshaling arguments for the proper use of armed force by Catholics. The result was intense piety, an interest in religious affairs, and religious propaganda advocating a just war to reclaim Palestine for the Christendom. The majority view was that non-Christians could not be forced to accept Christian baptism or be physically assaulted for having a different faith, although a minority believed that vengeance and forcible conversion were justified for the denial of Christian faith and government. Participation in such a war was seen as a form of penance which could counterbalance sin.
The status quo was disrupted by the western migrating Turks. In 1071 they defeated the Roman army at the Battle of Manzikert and the rapidly-expanding Great Seljuk Empire gained nearly all of Anatolia while the empire descended into frequent civil wars. One year later the Turks wrested control of Palestine from the Almohads. The disruption of pilgrimages by the Seljuk Turks prompted support for the Crusades in Western Europe.