It lies to the South of Tirmith, destroyed by the Tatars a short time ago. No doubt, the news of destroying Tirmith had reached the inhabitants of Balkh, who were extremely afraid of the Tatars. So, when the Tatarian army arrived near the city, the inhabitants asked for safety, and, unusually, the Tatars accepted to grant them safety, and committed neither robbery nor looting against them.

However, I was amazed by the behavior of the Tatars in this city of Balkh, and why they did not kill them as they used to do. However, some time later, this amazement was removed when I discovered that Genghis Khan returned to the city of Balkh once again and ordered its inhabitants to come with him to aid him to conquer another Muslim city, i.e. the city of Marw, as we shall see later.

Amazingly, the inhabitants of Balkh went forth with him to fight the people of Marw, although both were Muslims. In fact, the psychological defeat of the inhabitants of Balkh, caused by the atrocious hostilities committed in the neighboring city of Tirmith, led the inhabitants of Balkh to comply with the commands of Genghis Khan, even though they were to fight their fellow Muslims. In this way, Genghis Khan succeeded to spare his forces for other battles, and strike the Muslims with each other.

As amazing as this may seem to us, the same thing happens in our days in different parts of the Islamic world. The Americans used the inhabitants of North Afghanistan, the same region of Balkh, to fight the Muslims of Kabul in 2002; and they also used the Kurds of North Iraq to fight the other Iraqis; and there is no strength and no power save in Allaah.

https://en.islamstory.com/index.php/en/artical/20717/invasion-khuraasaan