Short answers, pulled from the story.
The Muslim conquests began in 642 AD after the battle of Nahāvand, with Herat and Sistan falling quickly to advancing Arab forces. These regions were among the first to be controlled by armies moving east from Iraq into central Persia.
Only 5,000 survivors reached Bust after suffering starvation and thirst in what became known as the Desert of Bust. The army was trapped in a valley by the Zunbils who lured them into inhospitable terrain before they could secure food or water.
Qutayba ibn Muslim led the final conquest of Balkh in spring 705, though accounts differ on whether the city surrendered peacefully or revolted. Four years later Tabari described the city as ruined following internal feuds among Arab troops until Asad ibn Abdallah al-Qasri restored it in 725.
Ya'qub ibn al-Layth killed both Salih b. al-Nadr and the last Zunbil king in 865 using treachery where his troops concealed lances behind horses while wearing mail under garments. This victory achieved through deception marked the end of centuries-long resistance in Zabulistan.
The Nuristanis remained politically independent until they were conquered and converted under Afghan Amir Abdul Rahman Khan between 1895 and 1896. Before this period they practiced ancient Hinduism infused with locally developed accretions.