Islam defeated the Visigoths in Spain (7C). Constantinople was cut off from the West.
Muslim troops gained control of Palestine in 636ADIn 1071 Muslims gained control over Anatoli (Turkey) and defeated the Byzantine emperor (East)The pope of the Eastern church appealed to Pope Gregory for help but didn't get any. Up until this point Islam respected Christianity because of the shared lineage
Crusades
Annotations:
The pope sought to undercut the power of monarchies in the small territories/countries and wanted to take control from the Monarchs to appoint bishops. Christians were very upset that the Holy Lands was taken by Islam and they were banned from going on pilgrimage.
The crusades started a 100 years of violence and knights were offered remission of sins because it was seen as 'Just War' (Augustine/City of God)
What is just war? Was it justified? Was it driven by a sense of piety or a sense of power?