The first Muslim threat to European entrenchment comes not from within Greater Syria but from Zangi, the emir of Mosul (in modern Iraq).

Zangi takes Edessa in 1144, and his son, Nur ad Din (light of the faith), secures Damascus, extending the realm from Aleppo to Mosul.

When the last Shia Fatimid caliph dies, Nur ad Din secures Egypt as well.

Eliminating Sunni-Shia sectarianism, the political rivalry that has so aided the European venture, he invokes jihad, holy war, as a unifying force for Arabs in Greater Syria and Egypt.

The jihad is to liberate Jerusalem, the third holiest city to Muslims, who call it Bayt al Quds (house of holiness) in memory of Muhammad's stopping there on his night journey to heaven.

It falls to Nur ad Din's lieutenant, Saladin (Salah ad Din al Ayubbi, meaning rectitude of the faith), to recapture Jerusalem.

Saladin, a Kurd, unifies Syria and Egypt, a necessary preliminary and, after many setbacks, captures Mosul, Aleppo, and the string of cities from Edessa to Nasihin.

In 1182 Saladin takes Al Karak (also known as Krak des Chevaliers), a Crusader fort on the route between Horns and Tripoli held by the infamous Reginald of Chatil lon, who has broken treaties, molested Saladin's sister, and attacked Mecca for the purpose of obtaining the Prophet's body and exhibiting it at Al Karak for a fee.

Saladin besieges Jerusalem on September 20, 1187, and nine days later Jerusalem surrenders.

Muslim Arab opposition to the Crusaders, initially fragmented among various petty states, begins, after 1128, gradually to unify under the strong leadership of the Turkish Zangid dynasty, which from 1127 to 1222 is to rule northern Iraq (al-Jazirah) and Syria.

Mahmud II rewards the loyal Zengi with the governorship of Mosul in 1127 following the failed rebellion of Caliph al-Mustarshid.

The key city of Aleppo submits to Zengi's authority to secure military protection against a possible Frankish crusader conquest.

Bohemond’s rule will be marked from 1128 by conflicts with Joscelin I of Edessa and skirmishes in the northern border.

Both Bohemond and Joscelin attack Aleppo individually, but refuse to cooperate in a larger siege against the city.

Roger of Salerno had given away territory to Joscelin, but Bohemond does not consider these donations legitimate as they had been made without his authority, even though he had been a minor at the time.

The dispute comes to open conflict between Antioch and Edessa, with Joscelin allying with the Muslims against Bohemond.

The Latin Patriarch of Antioch places an interdict over the County of Edessa.

Bohemond’s cousin Roger II invades and conquers Taranto in 1128, claiming it as the heir of William II of Apulia.

Bohemond, being away, can do nothing to prevent this.

This year, Baldwin II marches north to mediate in the dispute, and Joscelin abandons his claims.

Meanwhile, the atabeg Zengi consolidates his power over Aleppo and Mosul and the crusaders will never again have a chance to impose their authority over Aleppo.

Baldwin plans to attack Aleppo as well, but Antioch, which had passed to Bohemond II when he came of age in 1126, had begun to fight with Edessa and the plan fell through.

Aleppo and Mosul are united under the much stronger ruler Zengi in 1128, and Crusader control of northern Syria begins to dwindle.

Zengi, atabeg of Aleppo and Mosul, had allied with Taj al-Mulk Buri of Damascus against the crusaders in 1130, but this had been only a ruse to extend his power; he had had Buri's son taken prisoner and seized Hama from him.

Zengi had also besieged Homs, the governor of which had been accompanying him at the time, but could not capture it, so he returned to Mosul, where Buri's son and the other prisoners from Damascus had been ransomed for fifty thousand dinars.

Zengi had agreed in 1131 yo return the fifty thousand dinars if Buri would deliver to him Dubays ibn Sadaqa, emir of al-Hilla in Iraq, who had fled to Damascus to escape al-Mustarshid.

When an ambassador from the caliph arrived to bring Dubais back, Zengi had attacked him and killed some of his retinue; the ambassador had returned to Baghdad without Dubais.

Baarin, a village in northern Syria, serves in the early twelfth century as a fortress of the Crusaders, who refer to it as "Mons Ferrandus" or "Montferrand."

In 1133, Pons of Tripoli escapes to Baarin for refuge where, according to chronicler William of Tyre, he is shortly besieged by the Muslim army of Aleppo led by Zengi before being rescued by King Fulk of Jerusalem.

A civil war had broken out in the Seljuq western territories at the death of sultan Mahmud II in 1131.

Zengi had been recalled to the East by certain rebel members, stimulated by the Caliph and Dubais.

Defeated, Zengi had fled.

The Caliph al-Mustarshid had pursued him to Mosul, and besieged him there but without success for three months.

It had nonetheless been a milestone in the revival of the military power of the caliphate.

Zengi now resumes operations in Syria and in 1134 lays siege to Damascus, but is induced, partly by the bravery of the enemy, partly at the instance of the Caliph, to whom Zengi had made some concession in the public prayers, to relinquish the attempt.

Recalled again by troubles in the East, he will be unable to do much against the Crusaders until after al-Mustarshid's death.