Iraq Conquered by Khalid ibn Walid under Caliph Abu Bakr
After the Ridda Wars, a tribal chief of north eastern Arabia, Misnah ibn Haris, raided Persian towns in Iraq.
Misnah ibn Haris went to Medina to inform Caliph Abu Bakr about his success and was appointed commander of his people, after which he began to raid deeper into Iraq. Using the mobility of his light cavalry he could easy raid any town near the desert and quicky retreat into the desert, where the Sassanid army was unable to chase them. Misnah’s acts made Abu Bakr think about the expansion of the Rashidun Empire.
Abu Bakr started with the invasion of Iraq. Generations of Persian power and glory resulted in an irrational hatred and fear by Arab civilians and political elites. In return the Persians regarded the Arabs with contempt. To ensure victory, Abu Bakr decided on two measures; that the invading force would consist entirely of volunteers; and he put his best general, Khalid ibn al-Walid, in command of the army. After defeating the self-proclaimed prophet Musaylimah in the Battle of Yamama, Khalid was still at Al-Yamama when Abu Bakr sent him orders to invade the Sassanid Empire.
Making Al-Hirah the objective of Khalid, Abu Bakr sent reinforcements and ordered the tribal chiefs of north eastern Arabia, Misnah ibn Haris, Mazhur bin Adi, Harmala and Sulma to operate under the command of Khalid along with there men. In about third week of March 633 (first week of Muharram 12th Hijrah) Khalid set out from Al-Yamama with an army of 10,000. The tribal chiefs, with 2,000 warriors each, joined Khalid; Thus Khalid entered the Persian Empire with 18,000 troops. After entering Iraq with his army of 18,000, Khalid won decisive victories in four consecutive battles: Battle of Chains, fought in April 633 A.D; Battle of River, fought in the 3rd week of April 633 A.D; Battle of Walaja, fought in May 633 A.D (where he successfully used a double envelopment manoeuvre), and Battle of Ullais, fought in the mid of May, 633 A.D. By now the Persian court already disturbed by the internal problems, was down and out. In the last week of May 633 A.D, Hira capital city of Iraq fell to the Muslims after resistance in the Siege of Hira.
After resting his armies, in June 633 A.D Khalid laid siege of Al Anbar, which resisted and was eventually surrendered after a siege of a few weeks in July 633 A.D after the Siege of Al-Anbar. Khalid then moved towards the south, and conquered the city of Ein ul Tamr after the Battle of Ein ut Tamr in the last week of July, 633 A.D. By now, almost the whole of Iraq (Euphrates region) was under Islamic control. Khalid got a call of help from northern Arabia at Daumat-ul-Jandal, where another Muslim Arab general, Ayaz bin Ghanam, was trapped among the rebel tribes. Khalid went to Daumat-ul-jandal and defeated the rebels in the Battle of Daumat-ul-jandal in the last week of August, 633 A.D. Returning from Arabia, he got news of the assembling of a large Persian army. He decided to defeat them all separately to avoid the risk of defeat to a large unified Persian army.
Four divisions of Persian and Christian Arab auxiliaries were present at Hanafiz, Zumiel, Sanni and Muzieh. Khalid devised a brilliant plan to destroy the Persian forces. He divided his army in three units, and attacked the Persian forces in brilliantly coordinated attacks from three different sides at night, starting from the Battle of Muzieh, then the Battle of Sanni, and finally the Battle of Zumail during November 633 A.D. These devastating defeats ended Persian control over Iraq, and left the Persian capital Ctesiphon unguarded and vulnerable for Muslims attack, before attacking the Persian Capital Khalid decided to eliminate all Persian forces from south and west, he accordingly marched against the border city of Firaz, where he defeated the combined forces of the Sassanid Persians, Byzantine Romans and Christian Arabs in the Battle of Firaz in December 633 A.D. This was the last battle in his conquest of Iraq. While Khalid was on his way to attack Qadissiyah, a key fort in the way to Persian Capital Ctesiphon, he received the letter of Caliph Abu Bakr and was sent to Roman front in Syria to assume the command of Muslim armies to conquer Roman Syria.