Complex sentence: On 13 July 744, Nasr captured and imprisoned al-Kirmani, but when the latter escaped after barely a month, his rebellion was joined not only by Azd soldiers, but also by many of the Arab settlers around Marv.
Split into simpler sentences: On 13 July 744, Nasr captured and imprisoned al-Kirmani. After barely a month, the latter escaped, and his rebellion was joined not only by Azd soldiers, but also by many of the Arab settlers around Marv.