A pope had to sanction a war to qualify it as a Crusade.
The Turks had taken over Jerusalem in 1065, killing 3,000 Christians. Pope Urban II called for the first Crusade, which began in 1095 and ended in 1099. It succeeded in establishing the Latin Kingdom of Jerusalem. The final Crusade ended in 1291 with the fall of the city of Acre, the last Christian city to fall. According to some historians, the time of the Crusades extended to 1298, although 1291 is the traditionally accepted end.Learn more about Middle Ages