Aided by brilliant field commanders, he was able to incorporate present-day Iraq, Iran, Azerbaijan, Armenia, Georgia, Syria, Jordan, Palestine, Lebanon, Egypt, and parts of Afghanistan, Turkmenistan and south western Pakistan into the Caliphate.

A plan was agreed to launch a massive counterattack against Muslims in Iraq and Syria simultaneously to force them to retreat to Arabia where they could be dealt with later, either through invasion or economic blockade.

[10][6][9] When Abu Ubayda died in 639, Caliph Umar appointed Iyad in his place as the ʿamal (governor) of Hims, Qinnasrin (Chalcis) and al-Jazira with instructions to conquer the latter territory from its Byzantine commanders because they had refused to pay the tributes promised to the Muslims in 638.

[11] He encountered resistance from its defenders,[11] prompting him to withdraw and send smaller units to make raids around Raqqa, seizing captives and harvests.

[20] The counter sieges carried out by Iyad did not stop with Circesium and Hit, as Iyadh further sent Walid ibn Uqba to subdue the fortresses of the tribe of Rabi'a and Tanukhid.

[21] Between the end of 639 and December 640, Iyad and his lieutenants subdued, in succession, Circesium (al-Qarqisiya), Amid, Mayyafariqin, Nisibin, Tur Abdin, Mardin, Dara, Qarda and Bazabda.

[5][14] By the time the Christian Arab left, Khalid and his mobile guard had been reinforced by 4000 soldiers under Qa'qa from Iraq, and were now given permission by Abu Ubaydah to came out of the fort and pursue the enemy.

In the meantime, the Byzantine army split in two, one deployed at Maraj al Rome (Beqaa Valley) led by Schinos; the other, commanded by Theodras, stationed to the west of Damascus (Al-Sabboura region).

[29] Muslim victories pertinently ended Byzantine rule south of Anatolia, and Jerusalem fell in April 637 after a prolonged siege, Umar personally came to receive the key to the city by the Greek Orthodox patriarch, Sophronius, and was invited to offer prayers at the Church of the Holy Sepulchre.

It was exactly what Umar wanted,[31] as he is quoted saying I wish there were a wall of fire between us and the Romans, so that nor we can cross into their land neither they could in oursThe Byzantine empire already exhausted after major defeats in Yarmouk and Northern Syria was left vulnerable to Muslims' attacks and its very existence in Anatolia was threatened.

Moreover, Umar, due to his strong desire to consolidate his rule in the conquered land and owing to his non-offensive policy left the remaining Byzantine empire on its own.

After losing the Levant, the economic lifeline and main source of manpower of Byzantines and Armenia, Emperor Heraclius was left incapable of any military come back.

Initially hesitan, Umar rejected the proposal and is reported to have said "Life of my one soldier is dearer to me than a million Dirham.” However, he eventually decided to put the matter to the Majlis al Shura (parliament) in Madinah.

[citation needed] In of December 639 or early January 640, the Muslim army reached Pelusium, a garrison city considered to be the eastern gateway to Egypt at the time.

[56] However, during that night, the Byzantine Exarchate forces under commander named Arthabun (Aretion or Arteon in Latin), mounted surprise assault to the Rashidun camps.

[62] The 8,000 al-Aas soldiers were led by Zubayr, Ubadah, Maslama, Miqdad, Busr ibn Abi Artat and defeated the 20,000 strong Byzantine army under Theodore.

[Notes 5] As Shata has now converted to Islam, Miqdad now appointed him to lead the army to conquer the province of Sah, the fortresses in Ashmoun, Lake Burullus, and Dumayra.

Planned to overpower Umar, their common enemy, both emperors started preparations for a massive coordinated counterattack at once on their respected front to crush the threat in Arabia once for good.

Yazdegerd III, who unlike his Roman counterpart Heraclius, denied submission to Muslim supremacy in his land, was a constant threat to the Caliphate, and Umar decided to launch a whole scale invasion of Sassanid Persian to eliminate it.

[95] As the battle started, al-Qa'qa then execute the plan as he immediately galloped forward with his special units that included Amr on a daring charge to penetrate the surprised Sasanian lines.

to pass Sa'ad immediately sent a letter to Umar about further instruction, which replied by the Caliph for Sa'd to stay in al-Mada'in and appoint Hashim ibn Utbah as the leader of the troops to attack Jalula, Sa'ad immediately executed these instructions and sending Hashim ibn Utbah to lead the Rashidun troopes to engage Mihran forces in the battle of Jalula.

[89] The said composition of the overall Rashidun troops sent to Jalula numbered 12,000 soldiers, which consisted veteran warriors from Muhajirun and Ansar from the tribal chiefs of the interior Arabs.

[107] Before they engage Hormuzan, Arfajah and the Muslim armies marches to the vicinity of the area, to subdue several places including Kashkar, to cut off supply route and reinforcements for the Sassanids in Ahvaz.

[108] Umar giving specific instructed Abu Musa al-Ash'ari, the supreme commander of the Khuzestan conquest, to bringing in one of the caliphate best warrior, Al-Bara' ibn Malik, to the siege of Shushtar.

[129] Ahmed Cevdet Pasha, who narrated from the text of Al-Waqidi, pointed that Arfajah did not have trouble to raise an army and ships which needed to mount this naval invasion without the support of central caliphate, due to his notably wealthiness and powerful influence of followers from within his clan.

[139] Arfajah led the first Arab-Islamic naval campaign in history against Arab rebels on their own place in the final battle in Island of Darin (Qatif) [ar] and Juwathah.

[159] The Rashidun navy continued pushing as in 639 or 640, Ibn Abu-al-Aas and al-Hakam once again captured and garrisoned Arab troops in the Fars town of Tawwaj near the Persian Gulf coast, southwest of modern Shiraz.

[166][167][168] According to Baloch, the reasons Uthman ibn Abi al-'As launch this campaign without caliph consent were possibly zeal-driven adventures for the cause of jihad (holy struggle).

In accordance with the orders of Caliph Umar, the captured war elephants were sold in Islamic Persia, with the proceeds distributed among the soldiers as share in booty.

[177] The same year, in 644, Umar had already rejected the proposal by Ahnaf ibn Qais, conqueror of Khurasan, of crossing Oxus river in the north to invade Central Asia.