structural:summarization
Muslim revival (1131 to 1174)

On his deathbed Baldwin named Fulk, Melisende, and their infant son Baldwin III joint heirs. Fulk intended to revoke the arrangement, but his favouritism toward his compatriots roused strong discontent in the kingdom. In 1134, he repressed a revolt by Hugh II of Jaffa, a relative of Melisende, but was still compelled to accept the shared inheritance. He also thwarted frequent attempts by his sister-in-law Alice to assume the regency in Antioch, including alliances with Pons of Tripoli and Joscelin II of Edessa. Taking advantage of Antioch's weakened position, Leo, a Cilician Armenian ruler, seized the Cilician plain. In 1133, the Antiochene nobility asked Fulk to propose a husband for Constance, and he selected Raymond of Poitiers, a younger son of William IX of Aquitaine. Raymond finally arrived in Antioch three years later and married Constance. He reconquered parts of Cilicia from the Armenians. In 1137, Pons was killed battling the Damascenes, and Zengi invaded Tripoli. Fulk intervened, but Zengi's troops captured Pons' successor Raymond II, and besieged Fulk in the border castle of Montferrand. Fulk surrendered the castle and paid Zengi 50,000 dinars for his and Raymond's freedom. Emperor Alexios' son and successor, John II Komnenos, reasserted Byzantine claims to Cilicia and Antioch. His military campaign compelled Raymond of Poitiers to give homage and agree that he would surrender Antioch by way of compensation if the Byzantines ever captured Aleppo, Homs, and Shaizar for him. The following year the Byzantines and Franks jointly besieged Aleppo and Shaizar but could not take the towns. Zengi soon seized Homs from the Damascenes, but a Damascene–Jerusalemite coalition prevented his southward expansion.

Joscelin made an alliance with the Artuqid Kara Arslan, who was Zengi's principal Muslim rival in Upper Mesopotamia. While Joscelin was staying west of the Euphrates at Turbessel, Zengi invaded the Frankish lands east of the river in late 1144. Before the end of the year, he captured the region, including the city of Edessa. Losing Edessa strategically threatened Antioch and limited opportunities for a Jerusalemite expansion in the south. In September 1146, Zengi was assassinated, possibly on orders from Damascus. His empire was divided between his two sons, with the younger Nur ad-Din succeeding him in Aleppo. A power vacuum in Edessa allowed Joscelin to return to the city, but he was unable to take the citadel. When Nur ad-Din arrived, the Franks were trapped, Joscelin fled and the subsequent sack left the city deserted.

The fall of Edessa shocked Western opinion, prompting the largest military response since the First Crusade. The new crusade consisted of two great armies led overland by Louis VII of France and Conrad III of Germany, arriving in Acre in 1148. The arduous march had greatly reduced the two rulers' forces. At a leadership conference, including the widowed Melisende and her son Baldwin III, they agreed to attack Damascus rather than attempt to recover distant Edessa. The attack on Damascus ended in a humiliating defeat and retreat. Scapegoating followed the unexpected failure, with many westerners blaming the Franks. Fewer crusaders came from Europe to fight for the Holy Land in the next decades. Raymond of Poitiers joined forces with the Nizari and Joscelin with the Rum Seljuks against Aleppo. Nur ad-Din invaded Antioch and Raymond was defeated and killed at Inab in 1149. The next year Joscelin was captured and tortured and later died. Beatrice of Saone, his wife, sold the remains of the County of Edessa to the Byzantines with Baldwin's consent. Already 21 and eager to rule alone, Baldwin forced Melisende's retirement in 1152. In Antioch, Constance resisted pressure to remarry until 1153 when she chose the French nobleman Raynald of Châtillon as her second husband.

From 1149, all Fatimid caliphs were children, and military commanders were competing for power. Ascalon, the Fatimids' last Palestinian bridgehead, hindered Frankish raids against Egypt, but Baldwin captured the town in 1153. The Damascenes feared further Frankish expansion, and Nur ad-Din seized the city with ease a year later. He continued to remit the tribute that Damascus' former rulers had offered to the Jerusalemite kings. Baldwin extracted tribute from the Egyptians as well. Raynald lacked financial resources. He tortured the Latin Patriarch of Antioch, Aimery of Limoges, to appropriate his wealth and attacked the Byzantine's Cilician Armenians. When Emperor Manuel I Komnenos delayed the payment he had been promised, Raynald pillaged Byzantine Cyprus. Thierry, Count of Flanders, brought military strength from the West for campaigning. Thierry, Baldwin, Raynald and Raymond III of Tripoli attacked Shaizar. Baldwin offered the city to Thierry, who refused Raynald's demands he become his vassal, and the siege was abandoned. After Nur ad-Din seized Shaizar in 1157, the Nizari remained the last independent Muslim power in Syria. As prospects for a new crusade from the West were poor, the Franks of Jerusalem sought a marriage alliance with the Byzantines. Baldwin married Manuel's niece, Theodora, and received a significant dowry. With his consent, Manuel forced Raynald into accepting Byzantine overlordship.

The childless Baldwin III died in 1163. His younger brother Amalric had to repudiate his wife Agnes of Courtenay on grounds of consanguinity before his coronation, but the right of their two children, Baldwin IV and Sibylla, to inherit the kingdom was confirmed. The Fatimid Caliphate had rival viziers, Shawar and Dirgham, both eager to seek external support. This gave Amalric and Nur ad-Din the opportunity to intervene. Amalric launched five invasions of Egypt between 1163 and 1169, on the last occasion cooperating with a Byzantine fleet, but he could not establish a bridgehead. Nur ad-Din appointed his Kurdish general Shirkuh to direct the military operations in Egypt. Weeks before Shirkuh died in 1169, the Fatimid caliph Al-Adid made him vizier. His nephew Saladin, who ended the Shi'ite caliphate when Al-Adid died in September 1171, succeeded Shirkuh. In March 1171, Amalric undertook a visit to Manuel in Constantinople to get Byzantine military support for yet another attack on Egypt. To this end, he swore fealty to the Emperor before his return to Jerusalem, but conflicts with Venice and Sicily prevented the Byzantines from campaigning in the Levant. In theory, Saladin was Nur ad-Din's lieutenant, but mutual distrust hindered their cooperation against the crusader states. As Saladin remitted suspiciously small revenue payments to him, Nur ad-Din began gathering troops for an attack on Egypt, but he died in May 1174. He left an 11-year-old son, As-Salih Ismail al-Malik. Within two months, Amalric died. His son and successor, Baldwin IV, was 13 and a leper.