So you think that Roman Catholics aren’t Christians? Judge not that ye be not judged …
Medieval people were not so gullible that the Church authorities could ‘con’ them into doing something that they did not want to do. People went on crusade because they wanted to go, from a sense of duty to God, a desire to win honour and glory in the eyes of other people and win God’s favour, a desire for adventure, to see new lands, new civilisations, to boldly go (etc.,etc.), and because their friends and relatives were going, others expected them to go, their lord was going and expected them to accompany him … and so on. It is clear from warrior epics such as Beowulf and the Chanson de Roland that medieval warriors believed that they were fighting for God, even when their fundamental motivations for fighting seem to modern readers a long way from the standards of the New Testament. It was not necessary for the eleventh-century popes to invent the concept of fighting for God; the popes merely took advantage of the concept to encourage warriors to go to the assistance of the Byzantine emperor in his wars against the Muslim Turks in Asia Minor.