דברים, פרק כ׳, פסוק י״ב

When attempts at reconciliation are rejected, a military campaign must shift its approach, demanding an uncompromising stance against a hostile city. Refusing to make peace [אבן עזרא] is not merely a rejection of a treaty; it is a clear warning of future aggression. A city that declines a peaceful resolution poses a strategic threat, as leaving it alone would guarantee that it eventually initiates a war of its own [רש״י, אדרת אליהו]. The focus is deliberately placed on the city's own hostile posture, highlighting the inevitable future attacks expected from its inhabitants [משכיל לדוד].

Because of this looming threat, once a military campaign has begun, retreating is strictly forbidden. Leaving the area would only invite future provocations from the city's residents, making a siege an absolute obligation [העמק דבר, שפתי חכמים]. This requirement applies even if the city does not launch an active assault. The mere refusal to accept peace is enough to justify a siege, reflecting a conflict between two evenly matched forces [מלבי״ם]. The reality of this defiance can take different forms: the inhabitants might march out to engage in open combat, or they might simply lock themselves behind their walls, refusing to open their gates without ever stepping out to fight [רלב״ג].

In response to such stubborn resistance, the clear instruction is to establish a strict siege [ביאור שטיינזלץ]. This involves completely cutting off the city from the outside world, ensuring that no food or supplies can enter [רלב״ג]. The guidelines allow for severe and unyielding measures to break the enemy's resolve. This includes starving the inhabitants, cutting off their water supply, and even allowing disease to take its toll [רש״י, מלבי״ם, אדרת אליהו]. These intense pressures are to be maintained until God ultimately delivers the city into the hands of the Israelites [מלבי״ם].