According to Berzin, Umayyad interest in the region stemmed from their desire to control the trade route down the Indus River valley to the seaports of Sindh, an important link in the ancient Silk Road. They had earlier unsuccessfully sought to gain control of the route, via the Khyber Pass, from the Turki - Shahis of Gandhara. But by taking Sindh, Gandhara's southern neighbor, they were able to open a second front against Gandhara; a feat they had, on occasion, attempted before.

According to Wink, Umayyad interest in the region was galvanized by the operation of the Mids and others. Mids (a tribe of Scythians living in Sindh) had preyed upon Sassanid shipping in the past, from the mouth of the Tigris to the Sri Lankan coast, in their bawarij and now were able to prey on Arab shipping from their bases at Kutch, Debal and Kathiawar. At the time, Sindh was the wild frontier region of al-Hind, inhabited mostly by semi-nomadic tribes whose activities disturbed much of the Western Indian Ocean. Muslim sources insist that it was these persistent activities along increasingly important Indian trade routes by Debal pirates and others which forced the Arabs to subjugate the area, in order to control the seaports and maritime routes of which Sindh was the nucleus, as well as, the overland passage. During Hajjaj's governorship, the Mids of Debal in one of their raids had kidnapped Muslim women travelling from Sri Lanka to Arabia, thus providing a casus belli to the rising power of the Umayyad Caliphate that enabled them to gain a foothold in the Makran, Balochistan and Sindh regions. Also cited as a reason for this campaign was the policy of providing refuge to Sassanids fleeing the Arab advance and to Arab rebels from the Umayyad consolidation of their rule.

The campaign for the conquest of Sindh under Qasim was launched during the same period as the Umayyad conquest of Hispania and an offensive against the Kabul Shahan. It was a period of great expansion of the Umayyads under the governorship of Hajjaj, the first governor of both the Arabi and Ajami halves of the ex-Sassanid domains. Conflict was endemic among the frontier Muslims, with a considerable number seeking refuge with the king of Sindh. The period also experienced an intensification of the rivalry between Arab conquerors and the mawali; new non-Arab converts; who were usually allied with Hajjaj's political opponents and thus were frequently forced to participate in the Jihads on the frontier - such as Kabul, Sindh and Transoxania. Through conquest, the Umayyads intended to protect its maritime interest, while also cutting off refuge for fleeing rebel chieftains as well as Sindhi military support to the Sassanid rump state; akin to those received at several prior major battles during their conquest of Persia - such as those at Salasal and Qādisiyyah and finally at the Battle of Rasil. An actual push into the region had been out of favor as an Arab policy since the time of the Rashidun Caliph Umar bin Khattab, who upon receipt of reports of it being an inhostipable and poor land had stopped further expeditionary ventures into the region.

Muhammad bin Qasim's expedition was actually the third attempt, the first having failed due to stiffer - than - expected opposition as well as heat and exhaustion.

Hajjaj had put more care and planning into this campaign than the first campaign under Badil bin Tuhfa. Hajjaj superintended this campaign from Kufa by maintaining close contact with Muhammad bin Qasim in the form of regular reports and then regularly issuing orders. The army which departed from Shiraz in 710 CE under Muhammad bin Qasim was 6,000 Syrian cavalry and detachments of mawali from Iraq. At the borders of Sindh he was joined by an advance guard and six thousand camel riders and later reinforcements from the governor of Makran transferred directly to Debal by sea along with five catapults. The army that eventually captured Sindh would later be swelled by the Jats and Mids as well as other irregulars that heard of successes in Sindh. When Muhammad bin Qasim passed through Makran while raising forces, he had to re-subdue the restive Umayyad towns of Fannazbur and Arman Belah (Lasbela).

The first town assaulted was Debal and upon the orders of Al-Hajjaj, he exacted a bloody retribution on Debal by giving no quarter to its residents or priests and destroying its great temple in the process of freeing the kidnapped women. He then settled a garrison of four thousand colonists in one quarter of Debal, building a masjid over the remains of the original temple.

From Debal the Arab army then marched north taking towns such as Nerun and Sadusan (Sehwan) peacefully. Again the main temples were razed and masjid were built to replace them, often using their components; additionally one-fifth of the booty including slaves were dispatched to Hajjaj and the Caliph. The conquest of these towns was accomplished easily; however, Raja Dahir's armies being prepared on the other side of the Indus were yet to be fought. In preparation to meet them, Muhammad bin Qasim moved back to Nerun to resupply and receive reinforcements sent by Hajjaj. Camped on the east bank of the Indus, Qasim sent emissaries and bargained with the river Jats and boatmen. Upon securing the aid of Mokah Basayah, "the King of the island of Bet", Muhammad bin Qasim crossed over the river where he was joined by the forces of the Thakore of Bhatta and the western Jats.

At Ar-rur (Nawabshah) he was met by Dahir's forces and the eastern Jats in battle. Dahir died in the battle, his forces were defeated and a triumphant Muhammad bin Qasim took control of Sind. In the wake of the battle enemy soldiers were put to death - but not artisans, merchants or farmers - and Dahir and his chiefs, the "daughters of princes" and the usual fifth of the booty and slaves was sent on to Hajjaj. Soon the capitals of the other provinces, Brahmanabad, Alor (Aror) and Multan, were captured alongside other in between towns with only light Muslim casualties. Usually after a siege of a few weeks or months the Arabs gained a city through the intervention of heads of mercantile houses with whom subsequent treaties and agreements would be settled. After battles all fighting men were executed and their wives and children enslaved in considerable numbers and the usual fifth of the booty and slaves were sent to Hajjaj. The general populace was encouraged to carry on with their trades and taxes and tributes settled.

With Sindh secured Qasim sent expeditions to Surashtra, where his generals made peaceful treaty settlements with the Rashtrakuta. Muhammad bin Qasim wrote out letters to "kings of Hind" to surrender and accept Islam, and subsequently 10,000 cavalry were sent to Kannauj asking them to submit and pay tribute before his recall ended the campaign. The military strategy had been outlined by Hajjaj in a letter sent to Muhammad bin Qasim:

The Arabs' first concern was to facilitate the conquest of Sindh with the fewest casualties while also trying to preserve the economic infrastructure. Towns were given two options: submit to Islamic authority peacefully or be attacked by force (anwattan), with the choice governing their treatment upon capture. The capture of towns was usually accomplished by means of a treaty with a party from among the enemy, who were then extended special privileges and material rewards. There were two types of such treaties, "Sulh" or "ahd - e - wasiq (capitulation)" and "aman (surrender / peace)". Among towns and fortresses that were captured through force of arms, Muhammad bin Qasim performed executions as part of his military strategy, but they were limited to the ahl-i-harb (fighting men), whose surviving dependents were also enslaved.

Where resistance was strong, prolonged and intensive, often resulting in considerable Arab casualties, Muhammad bin Qasim's response was dramatic, inflicting 6,000 deaths at Rawar, between 6,000 and 26,000 at Brahmanabad, 4,000 at Iskalandah and 6,000 at Multan. Conversely, in areas taken by sulh, such as Armabil, Nirun, and Aror, resistance was light and few casualties occurred. Sulh appeared to be Muhammad bin Qasim's preferred mode of conquest, the method used for more than 60% of the towns and tribes recorded by Baladhuri or the Chachnama. At one point, he was actually berated by Hajjaj for being too lenient. Meanwhile, the common folk were often pardoned and encouraged to continue working; Hajajj ordered that this option not be granted to any inhabitant of Daybul, yet Qasim still bestowed it upon certain groups and individuals.

After each major phase of his conquest, Muhammad bin Qasim attempted to establish law and order in the newly conquered territory by showing religious tolerance and incorporating the ruling class – the Brahmins and Shramanas – into his administration.

Muhammad bin Qasim's success has been partly ascribed to Dahir being an unpopular Hindu king ruling over a Buddhist majority who saw Chach of Alor and his kin as usurpers of the Rai Dynasty. This is attributed to having resulted in support being provided by Buddhists and inclusion of rebel soldiers serving as valuable infantry in his cavalry heavy force from the Jat and Meds. Brahman, Buddhist, Greek, and Arab testimony however can be found that attests towards amicable relations between the adherents of the two religions up to the 7th century. Along with this were:

1. Superior military equipment; such as siege engines and the Mongol bow.
2. Troop discipline and leadership.
3. The concept of Jihad as a morale booster.
4. Religion; the widespread belief in the prophecy of Muslim success, as well as Dahir's marriage to his sister which alienated him from others.
5. The Samanis being persuaded to submit and not take up arms because the majority of the population was Buddhist who were dissatisfied with their rulers, who were Hindu.
6. The laboring under disabilities of the Lohana Jats.
7. Kind treatment of local population regardless of their beliefs.
8. Defections from among Dahirs chiefs and nobles.

After the conquest, Muhammad bin Qasim's task was to set up an administrative structure for a stable Muslim state that incorporated a newly conquered alien land, inhabited by non-Muslims. He adopted a conciliatory policy, asking for acceptance of Muslim rule by the natives in return for non-interference in their religious practice, so long as the natives paid their taxes and tribute. He established Islamic Sharia law over the people of the region; however, Hindus were allowed to rule their villages and settle their disputes according to their own laws, and traditional hierarchical institutions, including the Village Headmen (Rais) and Chieftains (dihqans) were maintained. A Muslim officer called an amil was stationed with a troop of cavalry to manage each town on a hereditary basis 

Everywhere taxes (mal) and tribute (kharaj) were settled and hostages taken - occasionally this also meant the custodians of temples. Non-Muslim natives were excused from military service and from payment of the religiously mandated tax system levied upon Muslims called Zakat, the tax system levied upon them instead was the jizya - a progressive tax, being heavier on the upper classes and light for the poor. In addition, three percent of government revenue was allocated to the Brahmins.

During his administration, Hindus and Buddhists were inducted into the administration as trusted advisors and governors. A Hindu, Kaksa, was at one point the second most important member of his administration. Dahir's prime minister and various chieftains were also incorporated into the administration.

The narrative in the Chach Nama conveys that Chach humiliated the Jats and Lohanas. Denzil Ibbetson records that "Muhammad bin Qasim maintained these regulations, declaring that the jats resembled the savages of Persia " According to Wink "While the Jats were also granted (aman) a considerable number of Jats were also captured as prisoners of war and deported to Iraq and elsewhere as slaves. No mass conversions were attempted and the destruction of temples such as the Sun Temple at Multan was forbidden. However, Qasim was not entirely deferential to the native religions. Many town temples containing idols were converted into mosques. At Multan, 6000 custodians of the Sun temple were made captive and their wealth confiscated. The temple housing the great idol (sanam) was a source of great wealth for the town, receiving pilgrims from across the region. Muhammad bin Qasim left the idol where it was;, but he hung a piece of cow flesh on its neck by way of mockery; he then built a mosque in the same bazaar at the center of the town. Again, this observation is generally disputed by Lane - Poole who writes that, "as a rule Mohammedan government was at once tolerant and economic".

A small minority who converted to Islam were granted exemption from Jizya. Hindus and Buddhists were given the status of Dhimmi (protected people).

An eccelastical office, "sadru-I-Islam al affal", was created to oversee the secular governors. While some proslytization occurred, the social dynamics of Sind were no different from other regions newly conquered by Muslim forces such as Egypt, where conversion to Islam was slow and took centuries.

Muhammad bin Qasim had begun preparations for further expansions when Hajjaj died, as did Caliph Al-Walid I, who was succeeded by Sulayman ibn Abd al-Malik, who then took revenge against all who had been close to Hajjaj. Sulayman owed political support to opponents of Hajjaj and so recalled both of Hajjaj's successful generals Qutaibah bin Muslim and Qasim. He also appointed Yazid ibn al-Muhallab, once tortured by Hajjaj and a son of Al Muhallab ibn Abi Suffrah, as the governor of Fars, Kirman, Makran, and Sindh; he immediately placed Qasim in chains.

There are two different accounts regarding the details of Qasim's fate:
1. The account from the Chachnama narrates a tale in which Qasim's demise is attributed to the daughters of Dahir who had been taken captive during the campaign. Upon capture they had been sent on as presents to the Khalifa for his harem. The account relates that they then tricked the Khalifa into believing that Muhammad bin Qasim had violated them before sending them on and as a result of this subterfuge, Muhammad bin Qasim was wrapped in oxen hides, and returned to Syria, which resulted in his death en route from suffocation. This narrative attributes their motive for this subterfuge to securing vengeance for their father's death. Upon discovering this subterfuge, the Khalifa is recorded to have been filled with remorse and ordered the sisters buried alive in a wall.

2. The Persian historian Baladhuri, however, states that the new Khalifa was a political enemy of Umayyad ex-governor Al-Hajjaj ibn Yusuf, Muhammad bin Qasim’s paternal uncle and thus persecuted all those who were considered close to Hajjaj. Muhammad bin Qasim was therefore recalled in the midst of a campaign of capturing more territory up north. Upon arrival, he was however promptly imprisoned in Mosul, (in modern day Iraq) and subjected to torture, resulting in his death.

Whichever account is true, is unknown. What is known however is that he was 20 years old when he was killed by his own Caliph. None have read the tombstone marking his grave for none know where he lies.

Muhammad bin Qasim had a son named Umro bin Muhammad who later became governor of Sindh.

There is controversy regarding the conquest and subsequent conversion of Sindh. This is usually voiced in two antagonistic perspectives viewing Qasim's actions:

His conquest, as described by Stanley Lane - Poole, in Medieval India (Published in 1970 by Haskell House Publishers Ltd), was "liberal". He imposed the customary poll tax, took hostages for good conduct and spared peoples' lives and lands. He even left their shrines undesecrated: 'The temples, he proclaimed, 'shall be inviolate, like the churches of the Christians, the synagogues of the Jews and altars of the Magians'. In the same text, however, it is mentioned that "Occasional desecration of Hindu fanes took place... but such demonstrations were probably rare sops to the official conscience..".

1. Coercive conversion has been attributed to early historians such as Elliot, Cousens, Majumdar and Vaidya. They hold the view that the conversion of Sindh was necessitated. Qasim's numerical inferiority is said to explain any instances of apparent religious toleration, with the destruction of temples seen as a reflection of the more basic, religiously motivated intolerance.
2. Voluntary conversion has been attributed to Thomas W. Arnold and modern Muslim historians such as Habib and Qureishi. They believe that the conquest was largely peaceful, and the conversion entirely so, and that the Arab forces enacted liberal, generous and tolerant policies. These historians mention the "praiseworthy conduct of Arab Muslims" and attribute their actions to a "superior civilizational complex".

Various polemical perceptions of Islam, Hinduism and Buddhism are also reflected in this debate. Elliot perceived Islam as a religion of "terror, devastation, murder and rapine" where the conquering Arabs were characterized as "ruthless bigots" and "furious zealots" motivated by "plunder and proselytism". The period of Qasim's rule has been called by U.T. Thakkur "the darkest period in Sind history", with the records speaking of massive forced conversions, temple destruction, slaughters and genocides; the people of Sindh, described as inherently pacifist due to their Hindu / Buddhist religious inclinations, had to adjust to the conditions of "barbarian inroad". On one extreme, the Arab Muslims are seen as being compelled by religious stricture to conquer and forcibly convert Sindh, but on the other hand, they can be seen as being respectful and tolerant of non-Muslims as part of their religious duty, with conversion being facilitated by the vitality, equality and morals of the Islamic religion. Citations of towns taken either violently or bloodlessly, reading back into Arab Sindh information belonging to a later date and dubious accounts such as those of the forcible circumcision of Brahmins at Deybul or Qasims consideration of Hindu sentiment in forbidding the slaughter of cows are used as examples for one particular view or the other.

Some historians strike a middle ground, saying that Qasim was torn between the political expediency of making peace with the Hindus and Buddhists; having to call upon non-Muslims to serve under him as part of his mandate to administer newly conquered land; and orthodoxy by refraining from seeking the co-operation of "infidels". It is contended that Qasim may have struck a middle ground, conferring the status of Dhimmi upon the native Sindhis and permitting them to participate in his administration, but treating them as "noncitizens" (i.e. in the Khilafat, but not of it).

Qasim's presence and rule was very brief. His conquest for the Umayyads brought Sindh into the orbit of the Muslim world.

The next Arab governor died on arrival. Dahir's son Jaisiah recaptured Brahmanabad and c. 720, he was granted pardon and included in the administration in return for converting to Islam. Soon, however, he recanted and split off when the Umayyads were embroiled in a succession crisis. Later, Junaid Ibn Abdur Rahman al-Marri killed Jaisiah and recaptured the territory before his successors once again struggled to hold and keep it. During the Abassid period, c. 870, the local emirs shook off all allegiance to the caliphs and by the 10th century the region was split into two weak states, Mansurah on the lower Indus and Multan on the upper Indus, which were soon captured by Ismailis who set up an independent Fatimid state. These successor states did not achieve much and shrank in size. The Arab conquest remained checked in what is now the south of Pakistan for three centuries by powerful Hindu monarchs to the north and east until the arrival of Mahmud of Ghazni.

Coastal trade and a Muslim colony in Sindh allowed for cultural exchanges and the arrival of Sufi missionaries to expand Muslim influence. From Debal, which remained an important port until the 12th century, commercial links with the Persian Gulf and the Middle East intensified as Sindh became the "hinge of the Indian Ocean Trade and overland passway."

Port Qasim, Pakistan's second major port is named in honor of Muhammad bin Qasim.

Yom-e-Babul Islam is observed in Pakistan, in honor of Muhammad bin Qasim.

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