The 3rd Rashidun Caliph, Uthman (r. 644–656) continued the policy of military expansion carried out by his predecessors, Umar and Abu Bakr.

During his reign, the caliphate stretched from Tripolitania, Egypt, and Anatolia to Greater Khorasan and Sindh and reached its greatest extent in 654 CE.

With the death of Umar and the disposal of 'Amr ibn al-'As from the governorship of Egypt, the Byzantines seized Alexandria, thinking it to be the right time to take action.

After re-conquering Alexandria, 'Amr ibn al-'As ordered the demolition of the walls of the city to obstruct any future invasion by Byzantine forces.

The success of these raids made Abdullah ibn Saad feel that a regular campaign should be undertaken for the conquest of North Africa.

Unable to storm the Byzantine fortifications, and satisfied with the huge amounts of plunder they had made, the Arabs agreed to depart in exchange for the payment of a heavy tribute in gold.

[1] Instead of annexing North Africa, the Muslims preferred to make it a vassal state and when the stipulated amount of the tribute was paid, the army withdrew to Barqah.

According to many books of Islamic history, the conquest of the Spanish section of the Iberian Peninsula is attributed to Tariq ibn-Ziyad and Musa bin Nusair in 711 – 712, in the time of the Umayyad Caliph, al-Walid I (Walid ibn Abd al-Malik).

However, according to Muslim historian Muhammad ibn Jarir al-Tabari,[2] Spain was first invaded some sixty years earlier during the caliphate of Uthman.

You will have your reward in this behalf both in this world and the next.No details of the campaigns in Spain during the caliphate of Uthman are given by Muhammad ibn Jarir al-Tabari or by any other historian.

The war ultimately ended in a baqt treaty, after the second battle of Dongola[4] Ten years later in 652, Uthman's governor of Egypt, Abdullah ibn Saad, sent another army to Nubia.

A major offensive into Cilicia and Isauria in 650–651 forced the Byzantine emperor Constans II to enter into negotiations with Caliph Uthman's governor of Syria, Muawiyah.

In 654–655 on the orders of Caliph Uthman, an expedition was preparing to attack the Byzantine capital Constantinople but did not carry out the plan due to the civil war that broke out in 656.

The first confrontation took place at Zaliq, a border town, during a Persian festival and with the Muslims victorious, the citizens asked for peace.

It is said that the Muslim commander, Rabiah ibn Ziyad, stuck a pole in the ground and asked the Persians to pile gold and silver up to the top.

Abdur Rahman ibn Sumrah led the army to Sistan, and, after crossing the frontier and overcoming resistance in the border towns, advanced to Zaranj.

Abdur Rahman ibn Sumrah made peace, with the Persians undertaking to pay an annual tribute of 20 million dirham.

After making these conquests, Abdur Rahman ibn Sumrah returned to the provincial capital Zaranj and stayed there as governor till the end of the caliphate of Uthman.

Khorasan, the province of the Persian Empire expanded from what is now north eastern Iran to western Afghanistan and southern Turkmenistan.

After the death of Umar, Khorasan broke into revolt under Sassanid Emperor Yazdgerd III (betrayed and killed in 651), before he could lead the Persians against the Muslims.

After consolidating the Muslim authority in Khorasan, Abdullah ibn Aamir crossed the Amu Darya (Oxus River) and invaded Uzbekistan in southern Transoxiana.

Details of these campaigns are not known but the source books tell us that a greater part of southern Transoxiana submitted to the suzerainty of Muslim rule.

Uthman sent his commander, Ubaidhullah ibn Ma' mar Tamini, to re-conquer Makran, along with other adjoining areas of Persia.

In early 644, Umar sent Suhail ibn Adi from Bosra to conquer the Kermān Province of Iran; of which he was made governor.

During Caliph Uthman's reign in 652, Balochistan was re-conquered during the campaign against the revolt in Kermān, under the command of Majasha ibn Masood.

In 654, Abdulrehman ibn Samrah was made governor of Sistan and an army was sent under him to crush the revolt in Zarang, which is now in southern Afghanistan.

At the same time another column moved towards the Quetta District in the north-western part of Balochistan and conquered an area up to the ancient city of Dawar and Qanzabil.

[10] By 654, the whole of what is now the Balochistan province of Pakistan was under the rule of the Rashidun Empire, except for the well-defended mountain town of QaiQan (now Kalat), which was conquered during Caliph Ali's reign.

[11] Abdulrehman ibn Samrah made Zaranj his provincial capital and remained governor of these conquered areas from 654 to 656, until Uthman was murdered.

Thereupon, Umar, after listening to the unfavourable situation for sending an army, instructed Hakim bin Amr al Taghlabi that for the time being Makran should be the easternmost frontier of the Rashidun Empire, and that no further attempt should be made to extend the conquests.