Zengi, Emir von Mossul

The next leader to emerge was Zengi, atabeg of Mosul. He was appointed to that position by the Caliph at Baghdad,  al-Mustarshid, in 1127. An atabeg is a Turkish term for a governor, something akin to a count (comes) in the Latin west. He expanded his rule to Aleppo in 1128 and captured Hama in 1129. This made Zengi the most powerful Muslim commander in Syria, though the Turks to the north were a constant threat to his position.

In the 1130s, Zengi was preoccupied with Damascus. In 1136, the Mamluk Bazawash occupied Damascus and began trying to expand into Palestine. It was he who killed Pons of Tripoli in 1137. Zengi saw Bazawash as a rival and tried to move against him. In general, over this period, Zengi's task was to expand southward while keeping his northern borders secure. It was a delicate balancing act.

He moved against Homs in June 1137, but Count Raymond of Tripoli advanced, forcing Zengi to raise the siege. King Fulk came up to help and Zengi won a great victory against the Christians, capturing the Count and nearly capturing Fulk.  The following year, though, Emperor John invaded in the north, attacking Aleppo itself, forcing Zengi to return to its defense. That same year, 1138, Zengi married Zumurrud, the mother of the atabeg of Damascus. He received Homs as her dowry, displacing Unur, the governor there. In exchange, Zengi sent Unur to rule in Damascus. In 1139, following the murder of the atabeg, Unur took over direct rule of Damascus as vizier. In some circles, Zengi was accused of having instigated the murder, but Unur proved to be an inconstant ally. By December 1139, Unur was in open revolt against Zengi's authority, and Zengi laid siege to the city, without success.

In March 1140, Unur sought alliance with Fulk of Jerusalem, leading to a battle in which Damascenes and Christians fought together against the Turk Zengi. They were able to force Zengi to retire to the safety of Aleppo and Unur actually paid a call on Fulk at Acre.