|The background: 11th century AD|
Many different factors contribute to one of the strangest threads in western medieval history. The story of the crusades is an exceptional blend of idealism and barbarity, even by the standards of other holy wars.
In the 11th century Europe is growing in confidence and wealth. The destructive raids of Vikings have ended, as the raiders themselves settle - in Normandy, Sicily and the British Isles. But by the same token the secular rulers of the time are confident, boisterous, unruly. Papal Rome is engaged in a long-term attempt to submit them to ecclesiastical authority. Involving them in a war for Christianity, under papal control, seems to offer a neat solution.
The idea of a crusade is already much in the air because of developments in Spain. The Spanish Christians have recently made rapid progress in their long attempt to reconquer their peninsula from the Muslims, and have then suffered equally rapid reverses - in a series of conflicts which have made El Cid something of a paragon as a Christian warrior.
The century also brings a provocation suggesting the need for a crusade to the Middle East. For centuries pilgrims from Europe have plodded slowly but safely through Byzantine Anatolia on their way to Jerusalem. But in 1071 the Turks defeat a Byzantine army at Manzikert and begin to occupy the entire region east of Constantinople. The pilgrim routes are no longer safe.