Crusades

Emperor Alexius wanted to gather support for his attempt to win back land from the turks - Trigger for Crusades 

Last Judgement - Heaven and Hell, this could be dealt with by paying penance of going on the crusade.

Huge levels of Religious enthusiasm - pilgrimages to Jerusalem.

Offered the chance of seizing land and gaining much wealth in the East.

Pope was looking to assert authority over Princes in the west ans eastablish his control over them.

Strong feudal sense of responsibility (to God) in protecting the holy land.

Leadership- effectively created successful military tactics despite the problems they had to overcome. The command structure was strong enough to overcome the personal rivalry for the Jerusalem. 

Spiritual Conviction- Main driving force for them, helped them overcome obstacles for the pursuit of Jerusalem. Successes along the way fueled the already intense religious zeal the crusaders possessed. 

Disunity of Muslim World- Sunni and Shiites, Turks and Arab. Turks were divided since the death of Sultan Malik Shah and the succession by Tutush and Barkiyarak.

Resourcefulness- useful especially along the journey to Anatolia, Supplies were gathered - Byzantines to the Genoese for the Siege of Jerusalem.