The matter of Muhammad's succession at his death in 632 had taken place at the Saqifah, a roofed building used by the tribe called the Banu Sa'ida, of the faction of the Banu Khazraj tribe of the city of Medina.

Abu Ubaidah ibn al-Jarrah had been there along with Abu Bakr and Umar.

Umar had told Abu Ubaidah to stretch forth his hand for the caliphate, but he had refused and said to Abu Bakr to stretch forth his hand to take the pledge of alliance.

After the Ridda wars, when Abu Bakr had sent Khalid ibn al-Walid to Iraq to conquer it, he had sent four Muslim armies into the Levant, making Abu Ubaidah commander of one of them.

Emessa had been selected as his target and he had been ordered to move through the Tabuk region after the army of Sharjeel ibn Hassana.

He remains commander in chief of the Muslim army until Khalid arrives from Iraq to Syria in 634.

Abu Ubaidah is ordered by Khalid to remain where he is until the latter reaches the Ghassanid city of Bosra, where they meet in June.

Khalid bin Walid writes to Caliph Abu Bakr, informing him of the progress of his operations since his entry into Syria, and sends one-fifth of the spoils which had been won during the past few weeks.

Hardly had Bosra surrendered when an agent sent by Shurahbil to the region of Ajnadayn returns to inform the Muslims that the concentration of Roman legions is proceeding apace.

Soon they will have a vast army of ninety thousand imperial soldiers at Ajnadayn.

Khalid ibn Walid orders all the Muslim corps in Syria to concentrate at Ajnadayn and on July 30, 634, defeats the imperial army in the Battle of Ajnadayn.

Abu Ubaidah had soon joined Khalid at the virtually impregnable fort of Chalcis, which had surrendered in June 637.

With this strategic victory, the territory north of Chalcis lay open to the Muslims.

Khalid and Abu Ubaidah continue their march northward and lay siege to Aleppo, which is captured after fierce resistance from desperate imperial troops in October 637.

The city reverts to the Semitic name of Halab.

The next objective is the splendid city of Antioch, the capital of the Asian zone of Constantinople’s empire.

Khalid and Abu Ubaidah decide to isolate Antioch from Anatolia before marching towards the city.

Accordingly, they send detachments north to eliminate all possible imperial forces and capture a garrison town, Azaz, fifty kilometers (thirty-one miles) from Aleppo; from here, the Muslims attack Antioch on the eastern side.

In order to save the empire from annihilation, a desperate battle is fought between the Muslim army and that of the defenders of Antioch, popularly known as Battle of Iron Bridge.

The imperial army is composed of the survivors of Yarmouk and other Syrian campaigns.

After being defeated, the imperial forces retreat to Antioch and the Muslims besiege the city.

Having little hope of help from Emperor Heraclius, Antioch surrenders on October 30, 637, with the terms that all imperial troops will be accorded safe passage to Constantinople.

The Islamic forces under Abu Ubaidah ibn al-Jarrah storm Caesarea Maritima, capital of Roman Palestine, and …

…effect their final capture of Ascalon.

Caliph Umar I stops the Muslim invasion and appoints Abu Ubaidah to the governorship of Syria.

The scholarly Jewish communities in Galilee have continued with varying fortunes under Roman rule and dominant Christian influence until the Arab-Muslim conquest of 638.

This period includes, however, strong Jewish support between 610 to 614 of the briefly successful Persian invasion.