Background

The Muslims armies were rapidly advancing in Syria. Emperor Hercules had fled to Antioch in Northern Syria. From there he organized an army to drive out the Arabs.

Conquering Damascus

Damascus was a flourishing and walled town of Syria. But the population itself was divided. Few religions were persecuted while the ones ascribing to Hercules were spared.
Arabs, in reality, didn’t invade them but liberated them. Their policy was much more lenient. Those that didn’t join Islam became Dhimmis.
The siege in 635 lasted about 2 months, when the citizens of Damascus finally gave up.
A treaty was signed that again showed the tolerant and merciful nature of Islamic State.
Khalid advanced forward and had now conquered every town between Damascus and Antioch. Most of the tribes submitted peacefully as we mentioned that it was more of a liberation than subjugation.

The Battle of Yarmuk (636)

Hercules collected a large army and placed it under his brother Theodore.
The desert of Syria is more o rocky nature. Yarmuk is one of the valleys there.
The battles saw small skirmishes for one month. It became full-fledged then.
Muslims won this battle too. There are few particular reasons why they won against such a gigantic army.
First, the Romans were divided among themselves. There were Greeks, Pagans, and Christians. The command of Theodore alienated few tribes’ chiefs too. Thus, it was a divided army.
Second, the desert favored Arabs, for they were desert dwelling people.
After losing the battle, Hercules fled to Constantinople.
Persians lost about 130-140k men while Muslims lost about 3k.

Khalid dismissed

Right after the victory, Khalid was relinquished of his supreme command position by Umar.
Some historians say that was because Umar had not forgiven Khalid for his mistreatment of Malik Nuwayra and his subsequent marriage to Malik’s wife.
Another incident was his refusal to clear how he gave a gift of 1000 dinar to a poet. Umar was a scrupulous man regarding the public money. Even though Khalid at last told him it was rom his own purse.
Whatever the reason, Khalid had conquered so much by then and had made a name for himself. Umar himself accepted this, “Khalid by winning such victories has made himself a commander. In fact, Abu Bakr was a better judge of other man than I.”
Muir has remarkably noted, “The military chief had to give place to the civil functionary; the sword to the pen; Khalid to Abu Obayda.”
By the end of 638, the conquest of Syria was complete under the supreme command of Abu Obayda.

Capture of Jerusalem

Only few towns like Jerusalem resisted the Arabs. They were inhabited more by Greeks than Syrian Arabs. Amr bin al-As made an advance and laid siege to the city.
The citizens soon found the resistance futile but agreed to surrender only if the Caliph himself came to take the keys.
The Caliph did come and set up an administration there. He returned to Madinah after a while.
The treaty signed in Jerusalem is called “the Treaty of Umar.” It is an epitome of tolerance and leniency. The Greeks were allowed to reside in Jerusalem, but they had to pay Jizya. Yet if they wanted to leave they would be allowed without any persecution.
After that few other towns were reduced by Amr and Muawiyah.

Plague of Amwas and Administration in Syria

An epidemic plague inflicted insurmountable losses on Muslims. The plague spread from Amwas. But it spread to number of other towns.
In total, it killed 25k people. It robbed many families. Umar went to Syria to look after the affairs for a while post-plague.
He before returning divided Syria into 4 military districts. As Abu Obayda and Yezid had died, Umar appointed Muawiyah as a Governor of Syria – the post he held till he became a Caliph himself nearly twenty years later.

For complete Islamic history notes click here.