שופטים, פרק י״א, פסוק כ׳

The military clash between the Israelites and Sihon, king of the Amorites, was rooted in deep distrust and strategic fears. Sihon completely refused to trust the Israelites and their stated intentions [ביאור שטיינזלץ]. When they asked for safe passage through his territory, he suspected it was a deceptive trap. He feared that their seemingly innocent request was actually a hidden plan to invade and conquer his land [מצודת דוד].

Beyond his personal suspicions, his aggressive response may have been tied to his official duties. As the regional border governor, he was responsible for defending the western side of the Jordan River against any raiders or looters approaching from the east [ביאור שטיינזלץ]. Driven by these heavy responsibilities and deep suspicions, he did not merely deny the Israelites the right to pass. Instead, he mobilized his nation and launched a direct military attack.