Many non-Muslims embraced Islam due to good conduct with them. Due to good conduct of Muslim army, the people of Sindh and Punjab kept practicing their local culture?
Muhammad bin Qasim was born around 695 AD. He belonged to the Saqqafi tribe; that had originated from Taif in Arabia. He grew up in the care of his mother; he soon became a great asset to his uncle Muhammad Ibn Yusuf, the governor of Yemen. His judgment, potential and skills left many other officers and forced the ruler to appoint him in the state department. He was also a close relative of Hajjaj bin Yousuf, because of the influence of Hajjaj, the young Muhammad bin Qasim was appointed the governor of Persia while in his teens, and he crushed the rebellion in that region. There is also a popular tradition that presents him as the son-in-law of Hajjaj bin Yousuf. He conquered the Sindh and Punjab regions along the Indus River for the Umayyad Caliphate.
There are both long and short term causes for the conquest of india. Arabs had trade with India and Eastern Asia. The trade was carried through sea rout; the rout was unsafe due to the plunder of the Pirates of Sindh. The Arab rebels also get refuge in Sindh. Thus the Umayyad wanted to consolidate their rule and also to secure the trade rout. During Hajjaj’s governorship, the Mids of Debal (Pirates) plundered the gifts of Ceylon’s ruler to Hijjaj and attacked on ships of Arab that were carrying the orphans and widows of Muslim soldiers who died in Sri Lanka. Thus providing the Umayyad Caliphate the legitimate cause, that enabled them to gain a foothold in the Makran, and Sindh regions.
The Umayyad caliphate ordered Muhammad Bin Qasim to attack over Sindh. He led 6,000 Syrian cavalry and at the borders of Sindh he was joined by an advance guard and six thousand camel riders and with five catapults (Manjaniks). Muhammad Bin Qasim first captured Debal, from where the Arab army marched along the Indus. At Rohri he was met by Dahir’s forces. Dahir died in the battle, his forces were defeated and Muhammad bin Qasim took control of Sind. Mohammad Bin Qasim entered Daibul in 712 AD. As a result of his efforts, he succeeded in capturing Daibul. He continued his Victorious Progress in succession, Nirun, fortress (called Sikka), Brahmanabad, Alor, Multan and Gujrat. After the conquest of Multan, he carried his arms to the borders of Kigdom of Kashmir, but his dismissal stopped the further advance. Now Muslims were the masters of whole Sindh and a part of Punjab up to the borders of Kashmir in the north. After the conquest, he adopted a conciliatory policy, asking for acceptance of Muslim rule by the natives in return for non-interference in their religious and cultural practices. He also established peace with a strong taxation system. In return he provided the guaranty of security of life and property for the natives. Hajjaj died in 714. When Walid Bin Abdul Malik died, his younger brother Suleman succeeded as the Caliph. He was a bitter enemy of Hajjaj’s family. He recalled Mohammad Bin Qasim from Sindh, who obeyed the orders as the duty of a general. When he came back, he was put to death on 18th of July, 715AD at the age of twenty.