It is not evident in medieval Muslim sources when Muhanna died or when the post of
amir al-ʿarab was stripped from him. In another version, Qutuz's successor
Baybars appointed Isa as a reward for assisting him during his 1250s exile in Syria (in this version, Ali was stripped of the title as punishment for denying Baybars refuge). which was separated from the
iqtaʿ of Hama,
Service with Baybars Isa's relations with Baybars were generally on good terms, though there were occasional exceptions. Following the Mongol destruction of the
Abbasid Caliphate of Baghdad in 1258, two Abbasid princes escaped; Abu al-'Abbas (later known as
al-Hakim), was the first to reach Syria under Isa's protection. However, the second surviving prince, Abu al-Qasim (known by the regnal name
al-Mustansir), was chosen by Baybars and inaugurated as the Abbasid
caliph in Cairo. Isa accompanied al-Mustansir on his Mamluk-sponsored campaign to reclaim Iraq from the Mongols. However, al-Mustansir was killed en route to
Baghdad in a Mongol ambush in October 1261. The next year, Isa was present in Cairo to bear witness that al-Mustansir's successor and kinsman, al-Hakim, was indeed a member of the Abbasid line. The strongest opposition came from Ahmad ibn Hajji of the Al Mira, relatives of the Al Fadl through their shared ancestor Rabi'ah ibn Hazim, whose descendants were collectively known as the Banu Rabi'ah. Ahmad ibn Hajji and his tribe were considered by the historians of their day as the kings of the Arabs (
muluk al-ʿarab) of the southern Syrian Desert, and Ahmad ibn Hajji led the struggle against Isa for the official post of
amir al-ʿarab. Ahmad ibn Tahir, whose demand of a share in Isa's
emirate was denied by Baybars, desisted from further opposition when he was given a smaller emirate elsewhere in Syria. In 1268/69, Baybars took hostage some of the Bedouin chieftains' sons as leverage to ensure that their fathers did not defect to the Ilkhanids. That same year, he halved Isa's annual grant of 130,000 silver
dirhams. News of this turn of events prompted Baybars to secretly rush to Syria from Egypt on 15 September 1270 and secure Isa's commitment to the Mamluks. He arrived in
Hama on 4 October and summoned Isa. Months later, in March 1274, Isa's forces confronted a group of
Khafaja Bedouin in Anbar, though there was no conclusive victory after a daylong battle. who was joined by Isa. The Ilkhanids and their Armenian and Georgian allies took advantage of the intra-Mamluk strife and an invitation by Sunqur to invade Syria, and sacked Aleppo. Isa persuaded Sunqur not to join the Ilkhanids and the latter escaped Qalawun's advancing army. Isa also sought to evade Qalawun's troops and barricaded himself in the desert fortress of
al-Rahba. Under his command were the horsemen of Al Fadl, Al Mira and
Banu Kilab among other Syrian tribes. It was during this counterattack that Isa's forces mounted a major assault against the Ilkhanid left ending in a rout. In reward for his performance, he was made the lord of
Palmyra in late 1281. ==Death and legacy==