The Arabs of the developing Rashidun Caliphate first reached Central Asia in the decade after their decisive victory in the Battle of Nahavand in 642, when they completed their conquest of the former Sasanian Empire by seizing Sistan and Khorasan.

Marw, the capital of Khorasan, fell in 651 to Abd Allah ibn Amir, and with it the borders of the Caliphate reached the Oxus (now called the Amu Darya).

[1][2] The lands beyond the Oxus—Transoxiana, known simply as "the land beyond the river" (mā wara al-nahr) to the Arabs[3]—were different to what the Arabs had encountered before: not only did they encompass a varied topography, ranging from the remote mountains of the Hindu Kush to fertile river valleys and deserts with oasis cities; they were also settled by a variety of peoples, both sedentary and nomadic, and instead of the imperial administration of the Persians, the region was divided into many small independent principalities.

[6] As the historian Hugh N. Kennedy remarks, "[Transoxiana] was a rich land, full of opportunities and wealth but defended by warlike men who valued their independence very highly".

[8][9] When the Chinese Buddhist monk Xuanzang visited Tokharistan in 630, he found no fewer than 27 different principalities under the overall authority of Tardush Shad at Kunduz, the Tokhara Yabghu or viceroy of Tokharia.

[13][12] Balkh, the ancient capital of the Greco-Bactrian Kingdom and the Kushan Empire, remained the most important settlement of the region and its main religious centre, with the famous Buddhist monastery of Nawbahar attracting pilgrims from far and wide.

[18] Rulership was hereditary, but an important role was played also by the landed gentry (dihqans) and wealthy merchants, who possessed, according to H. A. R. Gibb, "not only a large measure of independence but also on occasion the power to depose the ruling prince and elect his successor".

[23][24] During the 6th century, the Turks accumulated enormous quantities of silk given as tribute by the Chinese Northern dynasties, which the Sogdians endeavoured to sell west to the markets of the Byzantine Empire.

[28] The lively trade with and influence by the larger neighbouring civilizations meant that Sogdia was religiously varied as well; the country was largely Zoroastrian, but interspersed with native beliefs, as well as Buddhist, Manichaean and Syriac Christian communities.

[15][36] From its capital of Bunjikat, Usrushana was ruled by a series of kings bearing the title of afshin, nominally under Hephthalite and later Western Turkic suzerainty but practically autonomous.

As the historian Michael G. Morony emphasizes, their promises of tribute were more a "temporary expedient to secure their own positions, sometimes, against local rivals, with Muslim military backing", and not a firm commitment to the Arab cause.

Ibn Amir reacted with alacrity, sending generals to the region who scored some success—the rebel leader Qarin was captured or killed and Muslim armies campaigned as far as Bust and Zabul in what is now southern Afghanistan.

From 667 until he died in 670, Ziyad's deputy in Khorasan, al-Hakam ibn Amr al-Ghifari, led a series of campaigns in Tokharistan, which saw Arab armies crossing the Oxus into Chaghaniyan in the process.

Al-Hakam's death was followed by another large-scale uprising, but his successor, Rabi ibn Ziyad al-Harithi, took Balkh and defeated a revolt in Quhistan, before crossing the Oxus to invade Chaghaniyan.

In the following spring, Ubayd Allah crossed the Oxus and invaded the principality of Bukhara, which at the time was led by the queen mother or khatun, a Turkic title meaning "lady", as regent for her infant son Tughshada.

[55] Salm began a series of raids over the river, which ranged as far as Shash and Khwarizm (imposing a tribute of 400,000 dirhams on the region[45]), and again subdued Bukhara, which had rebelled again in the meantime.

The timing was favourable for the Arabs, since the Transoxianan princes could expect little support from elsewhere: the Khaganate had been destroyed, and the power of the nascent Tibetan Empire kept Chinese ambitions in Central Asia in check.

On the one hand, in a bid to keep the Arab settlers occupied and placate them with the prospect of plunder, they sought to conquer territory across the Oxus, but on the other, the volatile tribal politics doomed such efforts.

The latter now became a rallying figure for opposition to Umayyad rule: he was joined by aristocratic Iranian mawali, disaffected Arabs from Khorasan, 8,000 refugees from Ibn al-Ash'ath's failed anti-Umayyad uprising in Iraq, and gained the support of the prince of Chaghaniyan and Nezak Tarkhan of Badghis.

[78] The chief reasons for his success were his skill as an organizer, the unfailing support of al-Hajjaj, and Qutayba's willingness to work with and integrate the local population into the Umayyad administration.

This mass recruitment of local troops not only increased the manpower pool available, giving the Umayyad armies a significant numerical advantage, but also kept the native soldiery occupied far from their homes and employed for the Arabs' benefit, rather than posing a potential threat in their rear.

When the city rebelled, shortly after, he proceeded to punish it in exemplary fashion: men of fighting age were executed, the women and children sold off as slaves, and enormous booty amassed, especially in high-quality armour and weapons, which was used to equip the Arab army.

[91] As a result, al-Hajjaj drew up a new plan for his subordinate for the 709 campaigning season: the Arabs launched a direct attack on Bukhara, which caught the Sogdian alliance—possibly weakened by the death of its leader, the Wardan Khudah—by surprise.

[94] The year was too advanced for a direct confrontation and the Muslim levy-based army mostly disbanded, but Qutayba sent his brother Abd al-Rahman with the 12,000 men of the Marw garrison to Balkh, thus discouraging more native princes from joining the uprising.

[78][95] Lower Tokharistan was more firmly incorporated into the Caliphate, as Arab district representatives were appointed alongside the local princes, who were gradually relegated to secondary positions.

[95] From this point on, Balkh began developing "as a centre of Arab power and Islamic culture", in the words of C. E. Bosworth; within a generation, it was Islamicized to the extent of briefly replacing Marw as the provincial capital of Khurasan.

Later, in 712/13, Qutayba built a mosque in the city's citadel, but although the Arab authorities encouraged the conversion of the native population by paying them to attend prayers, Islamization proceeded slowly.

The Umayyad governor of Khurasan, Sa'id ibn Amr al-Harashi, harshly suppressed the unrest and restored the Muslim position almost to what it had been during the time of Qutayba, except for the Ferghana Valley, control over which was lost.

[citation needed] In 721, Turgesh forces, led by Kül Chor, defeated the Caliphate army commanded by Sa'id ibn Abdu'l-Aziz near Samarkand.

In 734, an early Abbasid follower, al-Harith ibn Surayj, rose in revolt against Umayyad rule and took Balkh and Marv before defecting to the Turgesh three years later, defeated.