Ahwaz was a place of strategic importance. It lay on the east bank of Karun river north east of Basra. It was the estate of Hormuzan one of the seven great chiefs of Persia.
Hormuzan had led a Persian contingent at the battle of Qadisiyya. When the Persians were defeated at the battle of Qadisiyya, Hormuzan managed to escape from the battle-field.
When the Muslim army under Sa'ad b. Abi Waqqas advanced to Ctesiphon the capital of Persia, the Muslim advance was resisted by the Persian force stationed at Babylon. One wing of the Persian force at Babylon was commanded by Hormuzan.
When the Persians were defeated at Babylon, the main Persian army withdrew to Ctesiphon, but Hormuzan with his contingent retired to Ahwaz.
When the Muslims captured Ctesiphon and later laid siege to Jalaula, Hormuzan with his base at Ahwaz sent raiding parties to different parts of Iraq occupied by the Muslims. These raids had sufficient nuisance value. One of the raids was led by Azeen the son of Hormuzan. In this raid Azeen was captured by the Muslims and killed.
After the death of Azeen, Hormuzan intensified his raids. These raids were conducted from two bases, namely Ahwaz and Manazir. The raids were conducted in the territory under the charge of Utba b. Ghazwan the Governor of Basra. As the raids were intensified, Utba asked for reinforcement from Ctesiphon. Saad sent a force under Noman b. Muqarrin. Meanwhile Utba recruited more warriors from the local Arabs.
Having received reinforcement, Utba declined to take the offensive against the raiding parties of Hormuzan. Two Muslim contingents advanced to the Persian bases Ahwaz and Manazir. One of these contingents was led by Noman and the other by Salma. The two Muslim forces launched a coordinated plan of attack, and the Persian force pulled back from the forward posts.
The Muslim detachments followed the retreating Persians and secured the right bank of the river Karun. The Persian forces stood on the left bank.
As the two forces faced each other on either bank of the Karun, the usual pre-war parleys began and emissaries went to and fro. The Muslims offered the usual three alternatives, conversion to Islam; payment of Jizya, and settlement through sword.
Hormuzan gave these alternatives due consideration. Wihh his experience of Qadisiyya and Babylon Hormuzan felt that the Persians were no match for the hardy Arabs. Settlement through the sword was likely to result in the defeat of the Persians. Hormuzan was therefore inclined to avoid war. Although Hormuzan believed in his heart of hearts about the truth of Islam, for political and other reasons he felt that at that stage he could not publicly accept Islam. He, therefore, agreed to the alternative of the payment of Jizya.
A treaty was executed between Utba and Hormuzan in November 638 whereby the entire princedom of Ahwaz came under the control of the Muslims. Hormuzan was to continue as the Governor and he was to pay a Jizya to the Muslims. The part of Ahwaz already occupied by the Muslims was to remain under the direct military rule of the Muslims. This area included the district of Manazir.
With the conquest of Ahwaz, the approach of Persian to the north of the Persian Gulf was completely cut off. The Muslims had now their firm hold on the delta area of the Tigris, the Euphrates, and the Karun.