The situation in the Islamic Near East

• Muslims had captured Palestine (including Jerusalem) from the Byzantine Empire as long ago as 637 at the battle of Yarmuk. Soon after the ruling Caliph ordered the building of the Dome of the Rock and the Aqsa Mosque on Temple Mount. (Christians had been using the Mount as a rubbish tip).
• In keeping with Muslim practice, the Christian and Jewish populations of Jerusalem were allowed to follow their own religion provided they paid a special tax called the Jizya.
• Meanwhile the Muslim Empire expanded so that by AD 750 it stretched from Iberia to north India. Muslims control most of eastern Anatolia and relatively stable relations with Byzantium ensued. The Byzantines had little desire to recapture Syria and Palestine. Christians pilgrims were free to travel there and traded freely with Muslims. 
• But in AD 989 the rival Fatimids (based in Egypt) took control of Palestine, creating instability and making pilgrimages more difficult, and a crisis occurred in 1009 when the deranged Fatimid ruler, Caliph Hakim, suddenly ended the toleration of Christians and burned the Church of the Holy Sepulchre. The crisis passed then Hakim died, but…
• By the mid 11th Century another group of (recently converted) Muslims had arrived from Central Asia – the Seljuk Turks. By the 1040’s they had captured Iraq and brought more instability to the region. In 1064 5,000 Christian pilgrims were brutally killed in an attack by the single Muslin tribesman. 
• The Seljuk Alp Arslan captured more territory in Byzantium at the Battle of Manzikert on 1071, then turned his armies south to capture Syria and Palestine from the Fatimids by 1087, creating further instability.

  Meanwhile, the Fatimids themselves disagreed over the choice of Caliph in 1094, prompting a split between the Ismailites and Assassins.