Why is Sindh known as Babul Islam?

Sindhi is known as Bab ul Islam, The Door to Islam, because Islam in Indian subcontinent

  was first introduced from Sindh. This was when Great young Muslim General Muhammad

 Bin Qasim conquered City of Deebal.

 He was sent from Arab to this area by his commanders. Having said that however many say

 that Islam was actually first introduced long time ago then this event; when many

 companions (Sahaba) of Prophet Rasool Allahsallalaho

sallalaho alley hi wassalam came here. Many say that there are still few graves of

companions of Rasool Allah salalahoalli wassalam in Sindh. 

As a side note there are many Awliya e Karam in Sindh as well from all famous Turooqs.

 Most prominently from Tariqah Aliya Naqshbandiya Mujaddadiya. Sheikh Hadhrat

 Muhammad Tahir Bakhshi, being the most prominent leader among those.

                                                                                                                                            Youm-i-Babul Islam was observed on Thursday in various districts of Sindh to commemorate the advent of Islam in the Indian subcontinent, with the arrival of Mohammad bin Qasim in Sindh at the port of Deebal on 10th of Ramazan.                                  

Jamaat-i-Islami Sindh and Jammt-i-Ulema-e-Islam (Fazal) held meetings and gatherings in Sukkur, Khairpur Shikarpur, Jacobabad, Ghotki, Kashmore, Noushehroferoze and other districts and towns to observe the Youm-i-Babul Islam.Different schools and institutions across the region, also held series of programs, to inform the students about the significance of the day. On the occasion students delivered speeches and actively participated in quiz programmes arranged by the Radio Pakistan Khairpur, Shah Abdul Latif University (SALU), Institute of Business Adminstration, (IBA) Sukkur, Ghulam Muhammad Mahar Medical College (GMMMC) Sukkur to highlight arrival of Mohammad bin Qasim in Sindh and the Muslim rule in India that followed, besides the movement initiated by Indian Muslims for independence.eferring to the fact that Sindh was called Babul Islam because the Muslims first landed here, she said that the people trumpeting their allegiance to Islam needed to actually practice the religion.

Director IBA Sukkur Nisar Ahmed Siddiqui termed Mohammad bin Qasim a great general who came for rescue of oppressed people and fought with terrorists and pirates.
Renowned scholar Maulana Asad Thanvi said that the conquest of Sindh by Mohammed bin Qasim was not for the territorial expansion of Muslim kingdom, but for abolishing tyranny, religious intolerance and class prejudices which were prevailing in Sindh at that time.
Describing the history of Sindh’s conquest, the speakers recalled that several expeditions were undertaken by Arabs, and finally Mohammad bin Qasim, a youth of 17, invaded Sindh with a force of 15,000 infantry plus horse and camel cavalry and was armed with five catapults, the largest of which took 500 men to operate.
He entered Sindh where we are present today commemorating the Youm-i-Babul Islam, they recalled.
Mohammad bin Qasim conquered and reorganized the whole of the country from the mouth of Indus to the borders of Kashmir, in a span of three years, from 712-15 AD, said Moulana Thanvi.