The battle of Yermuk was a historic battle which changed the course of history. When the news of the disaster of Yermuk were conveyed to the Byzantine emperor Heraclius at Antioch the capital of Syria, he at once decided to abandon Syria and withdraw to Constantinople. His parting words were "Farewell Syria! It is with great pain that I part from you. My salutations to thee O beautiful land."
From Yermuk, Abu Ubaida sent a detailed report of the victory of the Muslims to Umar along with the state share of the spoils of war. The message was carried by a highpowered delegation led by Hudheifa b. Al-Yaman. Umar had not slept for many nights anxiously awaiting news from Yermuk. As the news of the victory of the Muslims at Yermuk was intimated to Umar he had all the Muslims in Madina assemble at the Prophet's mosque, and a special thanks giving prayer was offered.
Umar in a letter addressed to Abu Ubaida congratulated him for the victory. He instructed that the cities in Syria like Damascus and Emessa which the Muslims had abandoned on the eve of the battle of Yermuk should be reoccupied. He further desired that after the withdrawal of the Byzantine emperor from Syria, the whole of Syria should be brought under Muslim control.
When the instructions of Umar were received, Abu Ubaidah left a few contingents in Jordan and Palestine and with the rest of the army marched northward. The city of Damascus opened its gates to the Muslims, and their return was enthusiastically welcomed.
From Damascus the Muslim army proceeded to Emessa. The people of Emessa also welcomed the return of the Muslims.
From Emessa a column under Khalid marched to Qinnissrin. Here a Byzantine force under Minas offered resistance to the Muslims. Khalid defeated the Byzantine army with great slaughter, and demolished all defensive works. There were many Arab tribes in the city. Khalid offered them Islam and they became Muslims. The other citizens agreed to pay Jizya. When the exploits of Khalid were reported to Umar, he acknowledged the services of Khalid in generous terms. He wrote "God bless Abu Bakr. He singled out Khalid for his favours and he was a better judge of men than me."
The victory of Qinnissrin cleared the way to Aleppo. Abu Ubaida accordingly marched to Aleppo at the head of the Muslim army. In the outskirts of Aleppo there were many settle ments of Arab tribes. They were offered Islam and accepting the offer they were converted to Islam. There was a Byzantine garrison at Aleppo which chose to shut itself in the fortifications. The city was besieged, and the Byzantines were forced to capitulate on the usual term of paying the Jizya.
From Aleppo the Muslim army marched to Antioch. It was the capital of the Byzantines in Syria. Although the emperor Heraclius had left for Constantinople, there was a sizable Byzantine garrison at Antioch. There was a large concentration of the Christians in the city. On the approach of the Muslim army the citizens of Antioch and the Byzantine garrison shut themselves within the fortified city. The Muslims besieged the city and blocked all approaches to the city. Within a few days the citizens suffered from the shortage of foodgrains and other provisions, and they capitulated agreeing to pay Jizya. With the capitulation of Antioch the Muslims were the masters of Syria. So great was the awe of the Muslim forces that wherever a few Muslim soldiers appeared the Christians waited on them and sued for peace.
After reducing Antioch, Abu Ubaida spread the Muslim forces in all directions. The neighbouring towns of Buqa, Jumah, Surmin, Tuzi, Quras, Tilghraz, Daluk and Ruban were captured one after the other without firing a shot. There was some show of resistance at Balis and Qasrin but such resistance was overcome by the Muslims without any difficulty. At Bughras a town on the border of Asia Minor there was a fierce conflict. The Muslim force under Habib b. Maslamah ultimately carried the town by assault. The people were killed in thousands and those who survived fled to seek shelter in Constantinople. Khalid led a campaign against Mara'sh. Here too there was a sanguinary battle. Brought to bay the Christians said that they were prepared to leave the city to the Muslims provided they were allowed to depart in safety. Khalid accepted the offer, and the Christians were allowed to escape to Constantinople without taking any property.
As a result of these campaigns, the Byzantines completely disappeared and Syria became a province of the Muslim dominions.
Abu Ubaida sent a detailed report to Umar about the conquest of Syria. Writing about Antioch, Abu Ubaida said:
"O Commander of the faithful, Antioch is a very beautiful and attractive place. Our soldiers were so much enamoured of the place that they insisted on staying there. I was afraid lest by staying there the Muslims might be involved in a luxurious way of living. I have accordiogly come back to Emessa along with the army. The Byzantine women are very handsome and the Muslim soldiers are very much attracted by them. They long to marry such women and that is a matter of headache for me".
In reply Umar congratulated Abu Ubaida for the victories that God had bestowed on the Muslims Umar appreciated Abu Ubaida's views about Antioch and his anxiety to pull out the Muslim soldiers from such a beautiful place lest they might be involved in a luxurious way of life. Umar, however, pointed out that God had not declared good things unlawful for the Muslims. God had said, "Avail of fine things, and do fine deeds. He also says, Oye faithful, out of the sustenance provided by Us eat delicious things, and offer thanks to Allah Who has provided you such delicacies." Umar added that it would have been advisable if he had allowed his soldiers to rest at Antioch for some time, but as he had pulled the Muslims from the attractive surroundings of Antioch with good intentions whatever he did was good. As regards the Byzantine women Umar said:
"Those who are unmarried let them marry Byzantine women provided they accept Islam. If any Muslim wishes to purchase a Byzantine woman as a slave let him do that for that is permissible."