In this excerpt from his manual on judicial practice, Abū Bakr Ahmad b. ʿAlī al-Jaṣṣāṣ (d. 370/980) discusses "different types of duties to fight based on residence: an enhanced duty existed for people in frontier lands bordering enemy territory as compared to those living in the interior." Like many medieval jurists, Jaṣṣāṣ "privileges the ruler’s authority to utilize the jihād duty" for a variety of reasons, including additional strategic objectives beyond territorial defense. He also states that if a ruler desires to offensively engage the enemy in their territory, then the obligation is on individuals. For more on jihād, read Adnan A. Zulfiqar's essay “Territory and Jurisdiction” in the Roundtable on the History of Islamic International Law on the Islamic Law Blog.