Why did Mohammed bin Qasim came to Pakistan?
An Arab trade ship was captured by Hindu pirates near the port
of Debal which is believed to be at or around modern Karachi. All
the occupants of the ship, including women and children, were made
hostages. One of those women's letter, believed to be written with
her own blood stating "Al-Madad Ya Hajjaj Al-Madad", was somehow
smuggled back to Hajjaj bin Yousuf in Iraq.
Hajjaj asked Dahir, the ruling Raja of Debal, to help him get
the hostages freed. Raja Dahir refused by saying he had no control
over pirates even they worked as his mercenaries. Muhammad bin
Qasim was the third general sent to defeat Raja Dahir when two
earlier generals died in battles.